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Pulse width modulation (PWM) is a method of reducing the average power delivered by an electrical signal, by breaking it up into predefined pulses. When utilized to operate direct acting solenoid valves, a PWM signal can result in significant power saving and heat reduction while maintaining the desired pneumatic function. This blog explains the PWM methodology, as it applies to direct-acting solenoid valves, and provides guidance in establishing the appropriate PWM parameters.
Figure-14
The arbitrary parameters illustrated above in Figure-14, describe two continuous hit and hold current values being supplied to the valve, (IMax) and (I5) respectively. In order to deliver the two separate input current levels, the power supply must be variable or the system must have two independent supplies delivering (IMax) and (I5). Given that both options are not ideal from a cost and power efficiency standpoint, the same power-saving gains can be realized by using a single/continuous DC power supply and adding a PWM, (pulse width modulation) circuit. The following example explains this concept in greater detail.
The average power consumed in this example can then be calculated by multiplying the square of average current, (IMAX x % duty cycle), by the coil resistance. {PAVG = IAVG2 x R = (0.100s x 0.50)² x 136 Ω = 0.34 W}.
End users should be aware that, although the theoretical/calculated hold power is equivalent in each case, (continuous supply and PWM), the actual power consumed at drop out may vary slightly. Therefore, it is important for the end-user to characterize the drop-out parameter utilizing the selected power saving method. Specific to the PWM method, this can be accomplished by simply reducing the duty cycle of the PWM hold signal until the drop-out condition is observed.
Figure-16 illustrates the output of an arbitrary duty cycle vs. valve state test. In this example, the drop-out condition is observed when the duty cycle is decreased to 40%. It should be noted that the duty cycle step sizes presented in this illustration are course and are intended for explanation purposes only. In practice, the duty cycle step size changes should be no larger than 1%.
Figure-16
It should be noted that the frequency of the PWM signal illustrated in Figures-15 and 16 is intended for instructional purposes only. Given the fast responding characteristics of a solenoid valve, the frequency of the applied PWM signal must be fast enough to prevent any mechanical oscillation of the armature; to prevent the mechanical components of the valve from chasing the oscillating electrical input signal. Specific to all solenoid valve platforms offered at Parker Precision Fluidics, PWM signals greater than 15KHz are typically recommended to prevent this condition from occurring.
Valve design/type considerations
Paker Precision Fluidics has been designing and building solenoid valves for over 25 years. Our engineers specialize in helping OEMs update original valves that are producing low yields. Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications. Call 603-595-1500 to speak with an engineer.
To learn more about Precision Fluidics' miniature solenoid valves, download the catalog.
This article was contributed by Phil Dodge, senior engineer at Parker Precision Fluidics.
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For proper connection and extra security, Parker Transair uses clamshell fittings for 3" (76mm), 4" (101mm), and 6" (168mm) aluminum pipes. These fittings are ideal for bigger diameters because they eliminate the need for push force (push-to-connect fittings) and hand torquing (snap ring fittings). These fittings can be installed using a battery operated or corded drill, saving time and reducing the chance for personal injury. Clamshell fittings use 4 bolts and a cartridge to make a tight seal between 2 sections of pipe, or a pipe and fitting. As with the rest of the Transair product line, minimal tooling and technical expertise are required for proper installation.
Clamshell connection technology is the last of the three connection technologies used on Transair aluminum pipe. The use of three different connection technologies ensures that ever diameter is safe, fast, and easy to install. Just like push-to-connect and snap ring, clamshell fittings are rated for compressed air, vacuum, and industrial/inert gases.
Installing CUT lengths of 3", 4", and 6" Transair Aluminum Pipe in eleven steps
By following these simple steps, you will be an expert installer of Transair clamshell fittings. Cut lengths of 3", 4", and 6" pipe requires you to follow 11 simple steps.
Our video shows you how:
1. Measure and mark the pipe for cutting
2. Cut the pipe
Place the pipe cutter (EW08 00 03) on the pipe at the desired cutting mark. Rotate the pipe cutter around until the pipe is cut After each full turn, gently tighten the wheel to tighten the cutting wheel. DO NOT use a hack or band saw to cut the pipe
3. Remove debris
Carefully chamfer the outer edge of the pipe using a file. Then, deburr the inner edge of the pipe using the deburring tool (6698 04 02).
4. Lug the pipe
Insert the appropriate lugging jaws (dependent on size) into the housing on the lugging tool (EW01 00 02). Next, place the jaws around the end of the cut pipe and pull the trigger to create the lug. This process needs to be completed multiple times to get a ring of lugs around the pipe. The suggested number of lugs is dependent on the pipe diameter. (see chart below).
CAUTION: DO NOT overlap the lugs!
5. Place the cartridge on the pipe
Slide the cartridge over the end of the pipe until it is stopped by the lugs.
6. Place the second pipe or fitting
Slide the second pipe or fitting into place until the cartridge meets the lug.
7. Position the clamshell fitting
Open the fitting, and position the clamshell over the assembly. The cartridge should fall in the middle of the connector.
8. Tighten the bolts
Using an Allen wrench, tighten the bolts in a cross pattern.
9. Pull the assembly
Grab the assembly on either side of the fitting and pull back away from the clamshell fitting.
10. Finish tightening the bolts
Using a drill, finish tightening the bolts using a cross pattern.
Transair Diameter Allen Wrench Size 3" (76mm) 6mm 4" (101mm) 6mm 6" (168mm) 8mm11. Install pipe hangers
To ensure the proper stability of the system, we suggest the use of at least two (2) hangers per pipe. Allow for a maximum of 16 feet of space between hangers for 20-foot lengths of pipe.
Installing FULL lengths of 3", 4", and 6" Transair aluminum pipe in seven easy steps1. Place the cartridge on the pipe
Slide the cartridge over the end of the pipe until it is stopped by the lugs.
2. Place the second pipe or fitting
Slide the second pipe or fitting into place until the cartridge meets the lug.
3. Position the clamshell fitting
Open the fitting, and position the clamshell over the assembly. The cartridge should fall in the middle of the connector.
4. Tighten the bolts
Using an Allen wrench, tighten the bolts in a cross pattern.
Transair Diameter Allen Wrench Size 3" (76mm) 6mm 4" (101mm) 6mm 6" (168mm) 8mm 5. Pull the assembly
Grab the assembly on either side of the fitting and pull back away from the clamshell fitting.
6. Finish tightening the bolts
Using a drill, finish tightening the bolts using a cross pattern
To ensure proper stability of the system, we suggest the use of at least two (2) hangers per pipe.
This post was contributed by Jim Tuma, marketing services manager, Parker Fluid System Connectors Division.
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When will my hose assembly fail? This may be the most common question when talking about hose assembly replacement. Sometimes hose assembly failures can cause serious damage and lead to costly downtime. Knowing what can cause a failure and having the exact hose replacement on hand will help you be prepared.
The surprise of a hose assembly replacement can be reduced by implementing a preventative maintenance schedule and by knowing how to recognize hose wear. There are several common factors that may cause problems with your hose assembly, you should look for these during your routine inspections.
1. Abrasion - Excessive rubbing of the hose against an external object or even another hose can wear away the cover and eventually the reinforcement layers. The cover is meant to protect the hose from the environment, so signs of damage to the cover or reinforcement layers should warn that failure is imminent.
2. Minimum bend radius - Hose assemblies can fail relatively quickly if the minimum bend radius is exceeded. For high pressure applications, premature failure could occur due to increased stress on the hose. In vacuum or suction applications, if the bend radius is exceeded, the hose may tend to be flat in the bend area. This will hinder or restrict flow. If the bend is severe enough, the hose may kink.
3. Heat aged - Overheating, from the internal hydraulic oil temperature or the external ambient temperature, will cause the hose to become very stiff. Overheating is accelerating when there is a hot internal fluid temperature and a hot external temperature. The inner tube will harden and begin to crack because the plasticizers in the elastomer will break down or harden under high temperatures. In some cases, the cover may show signs of being dried out.
4. Improper assembly - Contamination can be a result of poor assembly practices and can cause several problems for a hydraulic hose assembly. When cutting a hose, metal particles and debris can settle inside the hose if not properly flushed. This abrasive debris left in the hose will contaminate the hydraulic system. It can also cause small fractures to develop on the inner tube of the hose assembly, resulting in leakage.
5. Fluid compatibility - Incompatible fluids will cause the inner tube of the hose assembly to deteriorate, swell, and delaminate, The inner tube can also partially wash out in some cases. Verify that the fluid is not only compatible with the inner tube, but also the outer cover, fittings, and even O-rings.
6. Insertion depth - Fittings need to be pushed on completely to meet the recommended insertion depth. If the hose insertion depth is not met, fittings can blow off, leaving a failed hose assembly. The last grip in the fitting shell is essential to the holding strength.
7. Dry air / aged air - To avoid dry or aged air problems, confirm your hose is rated for extremely dry air. Hoses with inner tubes of PKR or EPDM rubber are preferred for these applications.
8. Tube erosion - Tube erosion is usually caused by a concentrated high-velocity stream of fluid or by small particles in the fluid. A hose assembly that is bent too tight for flow or an over abrasive medium for the inner tube can also lead to erosion.
Effective maintenance schedule
Your maintenance schedule should include checking hoses monthly, it is an easy way to catch issues with your hydraulic hose assemblies that may cause larger issues in the future. If you stick with it, frequently checking hoses will prevent your equipment from lengthy and expensive downtime.
The other piece of the puzzle is knowing the specifications of the hose assembly that needs to be replaced. Parker’s asset tagging and identification system, Parker Tracking Systems (PTS), is an efficient tool that can be integrated into your maintenance plan. Each PTS tagged hose assembly has a unique tracking number that provides the details of the hose assembly, so the PTS tagged hose assembly can be ordered without having to remove the part. PTS eliminates the need to wait for removal before the new part can be acquired. By reducing transaction time, customers can realize significant gains in productivity and increases invaluable up-time.
Replacement PTS tagged hoses now available for online orderingParker hydraulic hose replacement is easier than ever when you order your PTS tagged hose assembly online. Your PTS tag includes all of the configuration specifications you need.
Ordering is easy, start with your PTS ID number and have your hose replacement shipped to you.
Learn more about ordering hose assemblies online from Parker. Be prepared, hydraulic equipment that is taken care of will likely last longer.
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Hit and hold circuits enable solenoid valves to be energized to full power and held for a short duration of time before voltage and current are reduced significantly to lower levels, while still allowing the valve to remain open and energized. Hit and Hold circuits enable OEM system designers to operate solenoid valves at a reduced input voltage rating while maintaining the intended valve function. When implemented properly, significant power savings and heat reduction benefits can be realized in the application. The following blog explains the mechanical states of the valve when a power source is applied and instructs the end-user on how to determine an appropriate hold voltage parameter. Read Part 1 to catch up on Basic Solenoid Valve Operation
Reducing power consumption and heat generation within the valve
Now that we understand basic solenoid valve mechanics, how do these operating principles tie into reducing power consumption and heat generation within the valve? The key here is understanding the difference between the maximum current, at maximum rated voltage, and the current required to maintain the actuated state. A plot of the inductive response time of the valve is helpful in distinguishing the difference between the two states. Figure-6 below illustrates a typical electrical circuit for conducting a response time test and the resulting voltage vs. time plot captured on an oscilloscope.
Figure-6: Response time test circuit and typical oscilloscope output
It should be noted that to provide a clean voltage signal to the oscilloscope, a low resistance resistor, resistor-2 or R2, must be added to the circuit. (R2 Ė 1% of R1). Once the manual switch is closed, the voltage across R2 increases linearly until the armature begins to move as illustrated in Figure-7 and 8 below.
Figures-7 and 8: Oscilloscope outputs
Once the armature is in motion, the inductance of the circuit increases and the voltage signal across R2 begins to decrease until the armature is fully actuated (Figure-9). Once fully actuated, the input voltage across R2 returns to the same increasing trajectory until a steady-state, the maximum voltage/steady-state condition is achieved (Figure-10).
Figures-9 and10: Oscilloscope outputs
It is important to understand that the voltage required to actuate the valve will vary with changes in coil temperature and the coil resistance dependent on coil temperature. Therefore, as the coil temperature increases, the actuation voltage will increase proportionally to compensate for the increased coil resistance. The opposite is true when the coil temperature decreases. In either case, the actuation current will remain consistent with variations in coil and ambient temperatures.
For the remaining portion of this discussion, the maximum voltage parameter will be replaced by the corresponding maximum current parameter so that the difference between the maximum current and the drop-out current can be assessed. Figure-11 below illustrates the location of the corresponding maximum current and actuation current parameters.
Figure-11: Response time plot
As discussed earlier, the valve will return to the nominally closed state when the power source to the coil is disconnected. Rather than suddenly disconnecting the source, if the input current is gradually decreased, the current at which the valve state change occurs can be determined. This current value is referred to as the drop-out current and is typically detected by monitoring flow rate across a normally closed orifice. Figure-12 illustrates arbitrary test results from a drop-out current test.
Figure-12: Drop-out current/valve state versus time
Once the actuation and drop-out current parameters are known, the end-user must establish a minimum hold current (MHC) specification for the application. The MHC must include a safety buffer which accounts for drop-out current performance variations due to application parameters including, but not limited to, system vibration, ambient temperature variation, elastomer swell (due to media compatibility and/or elastomer temperature), valve function/porting, and any other application parameters which influence the drop-out current. Figure-13 illustrates an arbitrary MHC value based on the established performance margin.
Figure-13: Drop-out current/valve state versus time
The maximum current (IMax) and drop-out current (I4) parameters illustrated in figure 13 are not specified given that they vary with valve type and application parameters. Therefore, in order to understand the power savings potential in a hit and hold application, arbitrary values will be selected for (I4) and (I5) in the following example.
Let us begin by considering a 13.6 VDC / 136 Ohm valve configuration. For discussion purposes, the coil resistance will remain constant. Therefore, we are effectively ignoring any self-heating and ambient thermal effects on the coil resistance. Based on the input voltage and resistance of the valve, the (IMax) value is calculated at 100mA. [I = V/R] The arbitrary values selected for (I4) and (I5) are 25mA, and 50mA respectively.
In this example, rated voltage is applied to the valve for a short duration, (typically less than 100 msec), to ensure actuation at 100mA, (IMax). Once actuated, the input current is reduced 50mA, (I5), and the valve remains in the actuated state. The input current/actuation state scenario described in this example is illustrated in Figure-14 below.
Figure-14: Hit and hold current state versus valve state
Given the arbitrary parameters above, we can now calculate and compare the power consumed by the valve at the selected current states, {(IMax) and (I5)}, using the power equation P = I2R. During the initial “hit” current state, (IMax = 100 mA), the effective power consumed by the coil is 1.36 Watts; this calculation is based on nominal 136 Ohm resistance. Once the current is reduced to the MHC or “hold current” value, (15 = 50 mA), the power consumed by the valve effectively drops to 0.34 Watts. Again, this calculation is based on a constant 136 Ohm coil; there is no change or increase in resistance due to the internal heating of the coil. Comparing the two power states in this example, the end-user has effectively reduced the continuous power consumption of the valve by 75% while maintaining the desired function.
It is important to understand that the pull-in response or response time of the valve will vary within the same valve family due to the differences in valve types, (2/3-way normally closed, 2/3-way normally open, distributor or directional, and universal type configurations), and variations in the magnetic gap. Therefore, in order to select a proper hit current duration, the end-user should reference the response time specification of the valve prior to designing the circuit.
Now that we understand a method to characterize the actuation and drop-out parameters of the valve and have reviewed a theoretical/arbitrary example for power savings, we can now discuss optimum strategies for implementing “hit and hold” power delivery.
Paker Precision Fluidics has been designing and building solenoid valves for over 25 years. Our engineers specialize in helping OEMs update original valves that are producing low yields. Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications. To learn more about Precision Fluidics' miniature valves, flow controllers, pumps and accessories, please visit our website, or call 603-595-1500 to speak with an engineer.
This article was contributed by Phil Dodge, senior engineer at Parker Precision Fluidics.
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Parker's unrivaled industrial distribution network extends to approximately 13,000 locations globally. Through this extensive network of local, independent businesses, Parker brings its products and services to customers in 104 countries. Flux Active Service is a Parker distributor located in Stavanger, Norway, providing hose, couplings and related services for fluid power, power and control solutions for the oil and gas sector and maritime industry.
In March 2020, as the global pandemic caused major disruptions in the United States, Flux Active Services placed an order with Parker's Parflex Division for an 88 line, 2,000 ft. blowout preventer (BOP) umbilical and 300 ft. jumper bundle. These essential products are critical to drilling operations as they control the blowout preventer on the seafloor. The bundles were mutually agreed upon for an August delivery. As time progressed, the end customer moved up the timeline noting that they needed the products much quicker due to an active drill project.
Parflex responded to the customer's challenge by improving the delivery date by more than 30 days, The end customer booked a direct flight from Cleveland, OH to Stavanger, Norway for the product in late July. The logistics of moving a product like this was not a small task as the main umbilical is 13 feet wide, 11 feet tall and weighs 20,000 pounds. Due to the size or the product, the end customer contracted an Antonov 124 cargo airplane specifically for the transport of this product.
From start to finish, Parflex exceeded the customer's expectations, and is currently preparing to ship a second bundle for the same rig which will serve as a redundant back up that will also ship early and receive its own flight!
What is a BOP umbilical?The blowout preventer (BOP) is a critical piece of equipment in oil & gas drilling. The BOP resides on the wellhead on the seafloor and prevents the uncontrolled flow of fluids during drilling and completion. It essentially can seal the well if a back pressure spike (“kick”) is sensed and stop the flow to the surface which could cause severe damage. The BOP umbilical is comprised of smaller pilot hoses and at least one supply hose that are cabled together. The umbilical transmits hydraulic power and signals to the pilot valves on a BOP. A BOP usually has two sets of these pilot valves (“blue and yellow pods”) and thus two umbilicals.
Why Parflex hose for umbilicals?The Parflex Division is a leading manufacturer of thermoplastic hose. Thermoplastic hose is essential to a subsea umbilical due to several key reasons.
1. Length - In the case of these umbilicals, all of the pilot hoses and supply hoses were continuous, no splice fittings, over 2000ft.
2. Weight - These hoses are fiber reinforced and thermoplastic making them up to 70% less weight than a corresponding wire reinforced rubber hose.
3. Corrosion protection - The hose in the umbilical are fiber reinforced ensuring that there are not any hose elements susceptible to seawater corrosion.
4. Fluid compatibility - The core tube and cover of the hoses has compatibility with BOP hydraulic fluids and seawater
Visit our website to learn more about thermoplastics for hoses
The Parflex Division has a long history of manufacturing BOP umbilicals. These products have shipped for oil and gas drilling in Southeast Asia, Australia, Caspian Sea, and of course the Gulf of Mexico and the North Sea. Parflex has made subsea products up to 15,000 ft continuous length in the past. With the addition of HCR (high collapse resistant) hose, the capabilities and the applications that Parflex can service continues to expand.
Contributed by: Matt Peter, division marketing manager, Parflex Division
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Tractors, combines, wheel loaders, bulldozers, and excavators—you know, the big stuff— are called upon daily to perform the heavy lifting on the front lines of the agricultural and construction industries. Their job descriptions include tilling the soil, bringing in the harvest, building the roads, and anything else that contributes to meeting many of the world's most vital needs. Each of these machines is designed to perform specific jobs requiring many components to be in continuous motion.
Whether harvesting corn or preparing a construction site, that equipment is going to either lift, push, pull, or dig, so that means a hydraulic system is critical to the operation.
Small investment, huge return
If the hydraulic system is down, the equipment is out of operation and projects come to a screeching halt. A relatively inexpensive item, a check valve, can protect hydraulic system components worth significantly more, saving a business thousands of dollars in repairs and downtime. With both dollars and reputations on the line, the small but mighty check valve could be a lifesaver.
Before the 1960s, mobile equipment relied upon cables and pullies to get the job done. Since then, hydraulics took over, rendering today's machines more productive, durable, and cost-effective. The heart of the hydraulic system of this equipment is the pump. Its function is to get pressurized fluid to its assigned destination without interruption.
If the pump is malfunctioning, not only performance but also the safety of operators and other workers are at risk.
The last line of defense
In terms of protecting the integrity of a pump, the check valve is THE crucial component. It is the pump's last line of defense against damaging fluid backflow. A hydraulic system is a one-way street, and this valve is the traffic cop ensuring it stays that way.
For the level of protection provided, a check valve is remarkably simple in design, incorporating very few components—the body, poppet, spring, and retainer. The pressure of the fluid passing through the system opens the valve. Since it is a unidirectional flow device, the check valve keeps fluids moving in the desired direction. Also, it’s used in specific applications to maintain a system for optimum readiness and performance.
Protection and control
For mobile agricultural and construction equipment, in particular, the four most important functions of a check valve are:
Innovation + Design
Performance-conscious OEMs and end-users demand quality design and reliability. To this end, they turn to Parker. Long known for its innovative products and exacting standards, Parker check valves are engineered to perform under the most demanding conditions in which mobile agricultural and construction equipment operate.
Parker's check valves are available in various sizes, pressure ratings, flow capacities, and crack pressures, to meet the requirements of most hydraulic system applications.
• Parker's DT Series Check Valves cover the widest variety of applications out there. These hard seat check valves are offered in sizes from ¼" to 1-1/4" with the added benefit and convenience of compact design. Select sizes are also available in 45°, 90°, and tee shape fittings, which can help optimize system design by reducing labor and leak points. If you are unsure where to start looking for check valves, the DT Series is a great first option.
• Parker's CV Series Check Valves are another hard seat check valve option for your application. Built using a rugged, two-piece modular design, CV Series results in less pressure drop for increased performance in critical applications.
• Parker's CPIFF Series Check Valves are a soft seat check valve option for your application. The CPIFF valve’s poppet is streamlined with minimum restriction of flow in one direction. Flow is blocked in the reverse direction as the soft seat creates a leak-free seal in the closed position.
Parker maintains a large inventory of check valves in standard configurations for mobile agricultural and construction equipment that can be reviewed online.
Contributed by Lori Aus, senior product sales manager, Quick Coupling Division, Parker Hannifin.
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Solenoid valves are the most regularly used fluidics control component in the life science industry due to their high reliability, long life cycle, low power consumption, and compact design. In direct acting solenoid valve applications where battery life and/or heat generation is a concern, using a “hit and hold” electrical signal can result in significant power savings and heat reduction while still maintaining the required pneumatic function. To fully understand the benefits of hit and hold electrical control, let's take a deep dive into the basic functions of solenoid valves and the step by step process when an electrical potential is applied to the valve.
A typical direct acting solenoid valve is comprised of the following sub-components (see figure 1):
Figure 1: 2-way/2-position direct acting solenoid valve.
Note: Iron core/solenoid components are shown in blue. Pneumatic components are in green and the return spring is orange.
When an electrical potential is applied to the coil and current flows through the copper conductor, the coil component transforms into a magnet or solenoid. The magnetic field generated from the solenoid is then captured and directed through the iron core components of the valve as illustrated in figure 2.
Figure 2: Magnetic field captured and directed through iron core components
As the magnetic field is established, opposing magnetic poles are formed between the armature and pole subcomponents as illustrated in figure 3. (Also illustrated are the lines of magnetic force, or flux density, connecting the poles in green and blue).
Figure 3: Magnetic pole locations
The resulting magnetic force generated between these components is inversely proportional to the distance squared between the two components as illustrated in Figure-4. This distance is referred to as the magnetic gap.
Figure 4: Magnetic force on armature
When the magnetic force on the armature exceeds the installed load of the return spring, (and any supplemental pneumatic differential force), the armature will actuate/move to contact the pole as illustrated in Figure-5. Specific to the 2-way/2-position solenoid valve illustrated in Figure-5, once the actuation occurs, the fluidic path is opened between the valve ports.
Figure 5: Actuated valve state (open fluidic path)
To close the fluidic path and return the valve to a normally closed state, the voltage source is removed/disconnected from the coil. Once the power source is removed, the magnetic field collapses, and the spring returns the armature to the normally closed position.
It is important to understand that solenoid valves are current driven devices where the magnetic field strength of the solenoid is proportional to the amount of current traveling through the coil. Therefore, the two valve states described above, (actuation and drop-out), will ultimately be defined by the effective current traveling through the coil.
Now that you have an understanding of the basic solenoid valve operation, read the second part of this three blog series titled: Capitalizing on Valve Mechanics. This second part gives an in-depth understanding of how these principles tie into reducing consumption and heat generation within the valve.
Paker Precision Fluidics has been designing and building solenoid valves for over 25 years. Our engineers specialize in helping OEMs update original valves that are producing low yields. Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications. To learn more about Precision Fluidics' miniature valves, flow controllers, pumps and accessories, please visit our website, or call 603-595-1500 to speak with an engineer.
This article was contributed by Phil Dodge, senior engineer at Parker Precision Fluidics.
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There are several technology options in precision measurement devices but the two that have frequently been compared against each other are thermal mass flow and differential pressure mass flow. These technologies are widely used in high purity applications including semiconductor, analytical and medical. Manufacturers in these industries tend to focus on one technology or both. This white paper discusses the importance of thermal mass flow and laminar flow differential pressure mass flow instruments, the pros and cons of each, and a guide to help direct consumers toward the product that best suits their needs.
Thermal mass flow system
Figure 1 below shows a typical diagram of a thermal mass flow system. The temperature sensors used to measure the mass flow are wrapped around a stainless-steel flow sensor tube. Temperature measurements are taken at both heat sensors, heater 1 and heater 2 (see diagram). With no flow, the heat distribution along the sensor tube is balanced and the temperature difference between the two sensors is zero indicating no mass flow.
As fluid flow increases through the instrument, a portion of the flow is forced through the sensor tube by the pressure drop caused by the laminar flow element. Within the sensor itself, the temperature profile (heat distribution) moves downstream. The upstream sensor is cooled by the fresh gas entering the sensor, the gas carries heat from the upstream sensor element (heater 1) towards the downstream sensor element (heater 2). The increased flow will result in a greater temperature differential as the center of the heat distribution moves downstream. These distinct heat profiles are measured as temperatures at the sensors. The magnitude of the shift is proportional to the mass flow within the sensor.
The heat profiles are measured as changes in resistance with the individual windings wired across a wheathouse bridge to acquire a sensitive differential temperature measurement. The bridge's analog output is measured digitally and scaled to the 32,000-count digital output signal. In this way, the laminar flow element is used as a ranging element allowing gas and flow range flexibility so a unit can be scaled for each specific application. The laminar flow element device reduces the flow velocity to a laminar flow condition (Reynolds number <2000) by splitting the flow up into many equivalent parallel flow channels. The total number of channels in the laminar flow element determines the total gas mass flow through the metering section.
Differential pressure
.
The volumetric flow rate is calculated from this drop and the properties of the gas flowing through the unit. To calculate mass flow, the volumetric flow is converted to mass flow using gas properties and independent absolute pressure measurement, and an absolute temperature measurement. Once the three measurements are made and the analog signals are converted into digital signals the processor looks up the gas properties and applies them to the readings acquired to calculate the mass flow rate. The pressure-based mass flow device must accurately measure and convert 2 additional fluid properties (absolute pressure and absolute temperature) and maintain the metrology of 3 separate measurements over time. The ability to read the temperature, the common-mode pressure, the volumetric flow rate, and the mass flow rate can be beneficial in certain applications
Comparison of the two technologies Accuracy/warm-up time
Thermal mass flow devices using a bypass tube typically need a 30-minute warm-up time to achieve the full stated accuracy of ±0.5% of reading plus ±0.1% of full scale but the unit has relatively high accuracy prior to the 30-minute warmup being complete. Typically, the device can achieve an accuracy of ±2% of the reading almost immediately. Figure 3 shows the typical error for a thermal mass flow controller over time at room temperature, from a cold start-up. The graph shows that within 5.5 minutes the accuracy achieved by the unit is within the ±0.5% of the reading value. This is significantly shorter than the maximum recommended warm-up time of 30 minutes.
Compare this to a pressure-based laminar flowmeter that requires almost no warmup time but can only produce accuracies to ±0.8% reading plus ±0.2% of full scale. If the application calls for instantaneous full accuracy in seconds the pressure mass flow measuring device may be the better choice but if long term accuracy is the main objective, thermal mass flow is the best choice, especially if measurements can wait a few minutes.
Typically thermal mass flow devices are produced with a high level of particulate and chemical cleanliness. They are suitable for high purity applications including semiconductor, analytical, and medical applications. A material like 316L stainless steel or equivalent can handle many corrosive gases; this increases the cost but also ensures the product will function well over its working life. When purchasing a device look for the materials of construction (wetted parts) and compare their chemical compatibility to the gases they will be in contact with. Some thermal mass flow devices that use a bypass system offers a unique way of handling corrosive materials. The heat sensors are on the outside of the stainless-steel sensory tube (see figure 1), which provides a barrier between the sensor and the material being measured. Pressure differential measuring devices frequently have RTV-coated silicon-based pressure sensors inside the wetted flow path, which makes them very susceptible to corrosion, hydrogen embrittlement, or introduce unwanted chemistry to the flow stream. This can result in inaccurate readings or potential nonfunctioning parts of the device. If the application calls for the measuring of corrosive gases, look for the wetted materials to be a 316L stainless steel or equivalent and a thermal mass flow devices that use the thermal bypass system; this device is better equipped to handle corrosive gases and provide a cleaner output stream than a pressure-based mass flow device. Some differential pressure devices are available with stainless steel wetted materials to allow for compatibility with corrosive gases, but upgrading to that configuration can add significant cost. Pressure based mass flow devices compromise on materials for speed and sensitivity; this extra speed and sensitivity is desired in certain applications but may not be suitable for analytical and high purity applications flow devices.
Key takeaways
With the above breakdowns the biggest takeaways are:
When high accuracy, high-pressure capability, and compatibility with corrosive gases are the primary needs of your flow measure, thermal mass flow devices are the best solution. When it is critical that your device warmup time in seconds and accuracy and pressure is less of a concern, pressure mass flow devices are the better choice. This can vary with manufacturers, so be sure to do research and speak with the manufacturer’s application engineers.
Parker Precision Fluidics offers a wide variety of thermal mass flow meters and controllers for all your application needs. The new X-Flow™ is a new simplified mass flow controller for your instrument, lab, or process needs. X-Flow™ delivers fast, repeatable, and reliable high accuracy flow control through constant thermal by-pass mass measurement technology coupled with digital communication protocols. X-Flow™ is calibrated to your specific conditions and includes asset calibration management software. Other features include:
With over 30 years of experience with the mass flow technology, Parker Precision Fluidics offers guaranteed high quality, reputable products and market-driven innovation, helping our customers improve equipment accuracy and repeatability. Contact us today at ppfinfo@parker.com or call 603-595-1500 to speak to an expert applications engineer about your fluidic circuit needs.
This article was contributed by David P. Sheffield, senior product engineer at Parker Precision Fluidics. David has been a mechanical engineer for almost 30 years and has 10 years of experience in mass flow and mechanical flow measurement technology.
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Developing and introducing a new clinical diagnostic instrument or medical device is a challenging accomplishment that often takes years. One of the final steps in bringing life-saving, life-improving equipment to the public is US FDA listing and CE marking processes that ensure the safety of these devices as well as their compliance to well-established global standards. Trouble at this stage of the project can lead to frustrating and costly delays for medical device manufacturers. Examples of complications that may be found at this stage are electrical emissions or immunity issues that might only become apparent when all the pieces come together for final testing.
This blog explores standards required for the safety and performance of medical electrical equipment and discusses the benefits of choosing components, such as pumps, that are IEC-60601 compliant.
International Electrotechnical Commission
The International Electrotechnical Commission (IEC) is an organization that publishes international standards for all electrical, electronic, and other related technologies. In 1977, IEC published the IEC 60601 and it is continually updated as technology develops and improvements are made. Today, IEC 60601 is the international standard for the safety and performance of medical electrical equipment in most major countries. This standard is very important in that it provides compliance with US-FDA, Canada-Health Canada, and EEU Medical Device Directive 2007/47/EC regulations. IEC 60601 is currently in its 3rd revision (60601-1-11:2015) and certification can be obtained through an OSHA-approved testing laboratory.
Across the globe, medical regulating bodies, such as the FDA, EEU, and Canada-Health Canada, are responsible for ensuring the efficacy of the devices being designed and manufactured by OEMs. These regulating bodies have widely accepted the IEC-60601 standard as a benchmark for the basic safety and essential performance of medical electrical equipment for commercialization.
The 60601-1-11:2015 acts as risk management for the product design, manufacture, and intended use by requiring safety by design with protective measures in the medical device and calling for instructions or safety labeling. This standard provides customers with the assurance that the product is safe and reliable.
Products that fall under IEC-60601
There are two types of products that fall under IEC-60601: Medical electrical equipment and medical electrical systems. Medical electrical equipment is defined as:
“Equipment, provided with not more than one connection to a particular supply main and intended to diagnose, treat, or monitor the patient under medical supervision and which makes physical or electrical contact with the patient and/or transfers energy to or from the patient and/or detects such energy transfer to or from the patient”.
— IEC 60601-1 subclause 2.2.15
A medical electrical system is defined as:
“Combination, as specified by its manufacturer, of items of equipment, at least one of which is Medical Equipment to be inter-connected by functional connection by use of a Multiple Socket-Outlet”.
— Nicholas Abbondante, chief engineer, EMC Testing for medical devices, Intertek Group, plc.
Why choose components that meet compliance standards?
When selecting a component for your device, it is important to research the required standards. The IEC-60601-1-2 is the standard mandating that EMC testing is performed on any electronic medical device, which ensures that a device meets necessary emissions and immunity standards by the FDA to sell the device.
For medical device manufacturers, partnering with a supplier that offers compliant components, improves efficiency and reduces costs. Requesting a component manufacturer to obtain the specific compliance standards can result in expensive delays in the project scheduling process.
Miniature pumps, for example, are critical electromechanical components frequently used in medical devices. Pumps needed in today’s medical equipment range from simple on/off devices that are used for a very short time frame to dynamic control devices that need to last several years of continuous operation.
The new BTX-Connect diaphragm pump from Parker Precision Fluidics has been tested to IEC-60601-1-2 standards to provide a seamless approval process for the completed device.
Specifically, the BTX-Connect miniature diaphragm pump was tested and passed the following standards and tests:
The BTX pump uses brushless DC motor technology for maximum reliability and control. The controller offers the most dynamic control range and communication capability available. This electrical component of the pump is subject to electromagnetic emissions and immunity, the very same as the medical equipment system of which it becomes a part. Other features include:
This blog was contributed by Chris Osborne, application engineer, Parker Precision Fluidics. 
Highways, city streets and parking lots lay bare. Rush hour and stop-and-go have come to a virtual gridlock. For tens of millions of people across the U.S., arriving to work on time is a whole lot easier and less stressful, except for those days when a detour is necessary to get around the unexpected pileup of kid’s toys blocking the exit to your home office.
Daily life has changed: how we interact with family and friends, how we learn, how we shop and how we work are different. They involve putting some space between others and us. Businesses around the world have transitioned from large, robust facilities to the friendly confines of the home office. While temporary at first, companies in sectors such as technology and e-commerce may allow working remote to become permanent.
Data centers put to the test
Roadways and byways may be desolate, but the traffic is moving fast across data centers. These coliseums of information and data are being inundated with massive surges in internet usage, with increase estimates ranging between 50 and 70 percent, as everyday life transitions to home life. The geographic shift of internet demand from city centers to neighborhoods is validated by major cities across the globe, from San Francisco to Sydney, revealing the change in internet traffic between January and March 2020.
Data has never been more important than right now. It’s the lifeblood of today’s first responders and medical professionals, businesses, education, entertainment and nearly every industry on the face of this planet. Everyone, and we do mean everyone, is relying on the internet and communication networks to continue business as normal under the most unique circumstances. The COVID-19 global pandemic has highlighted the importance of data centers and the ability to take on this sudden rush of information.
Decades of planning and preparation
So, how have data centers been able to handle such a spike in internet traffic? You have to go back nearly 60 years to find the answer. In the early 1960s at the height of the Cold War, the only network people knew about was the telephone system. It was powerful, but in the same breath, expensive, fragile and uncompromising. Researchers began working on a new network – one that would be flexible and handle different types of communication, including data, voice and video. The data center was born.
Over time, as networks grew, so too did data centers to accommodate new demands. ARPANET, office and home computers and the internet came in increments and at each digital revolution, the network became more reliable to manage the increase in data capacity. And so 2020 happened, data centers across the world weren’t shook, but prepared for this moment.
Data centers staying cool under pressure
Capacity management is critical to all fundamentals of any organization. Data centers are performing efficiently and more effectively with no constraints. This level of operation comes on the heels of supply chain disruptions, reduced staffing and social distancing guidelines.
The infrastructure of data centers has played a vital role in keeping cool under intense pressure. Traditional air-based cooling systems have been replaced with innovative liquid cooling capabilities to reduce energy consumption and meet power demands. Plus, address limitations of water usage that can greatly affect the ability to utilize evaporate cooling and cooling towers in order to carry off heat generated through a facility.
The future of data centers during the COVID-19 pandemic
Fluid connections are critical in network communications and liquid cooling systems; both go hand-in-hand and will play vital roles over the course of this pandemic. In terms of infrastructure, liquid cooling quick disconnects feature a state-of-the-art internal design and flush-face valves, which reduces pressure drop and virtually eliminates drips during connection and disconnection. This capability means investments in reliable connections pay big dividends in the short and long-term future.
The pandemic has shown us that connectivity is a must. As more aspects of our daily lives transition to home, from work and school to shopping and entertainment, data centers will continue to adjust to this increase demand for connectivity and capacity.
This article contributed by Todd Lambert, market sales manager, Parker Hannifin Corporation's Quick Coupling Division.
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This blog is part three of a three-part series that comprises a complete white paper "Efficient and Effective Direct Acting Solenoid Valve Control: The Benefits of Using Hit and Hold Electrical Control on Direct Acting Solenoid Valves". Download a copy here.
This blog is part three of a three-part series that comprises a complete white paper "Efficient and Effective Direct Acting Solenoid Valve Control: The Benefits of Using Hit and Hold Electrical Control on Direct Acting Solenoid Valves". Download a copy here.
Request a sample and get technical specifications for the IEC-60601-1-2 compliant BTX-Connect miniature pump
To find out more about the BTX-Connect miniature pump, visit our website and request a sample