Technologies

Safety and performance are top considerations when using hydraulic hose. To guarantee productivity and prevent potential hazards in the work environment, proper installation is imperative. A safe work environment and desired performance both require proper hydraulic hose routing, and these helpful installation tips are one way to ensure efficiency and help prevent premature hose failure.

The routing of a hose assembly and the environment in which the hose assembly operates directly influence the service life of the hose assembly. Proper routing of hose assemblies will maximize service life and ensure a safe working functionality.
 

Ten tips for safety and performance

1. Allow for Slack: Use tools that provide enough slack to allow for changes in length to occur when hose is pressurized. Hydraulic hose is capable of elongating up to 2% or contracting up to 4%, depending on construction. The hose length must be determined so that the hose assembly has enough slack to allow the system components to move or vibrate without creating tension in the hose. The service life of hose is reduced if hose assemblies do not permit adequate flexing and allow for length changes due to expansion or contraction. When pressurized, a hose that is too short may stress the hose fitting connections or pull loose from its fittings, causing premature metallic or seal failures. It is important not to allow too much slack and therefore introduce the risk of the hose snagging on other equipment or rubbing on other components.
    
2. Do Not Exceed Minimum Bend Radius: Use tools to avoid exceeding the minimum bend radius. Bending hose beyond the recommended bend radius places excessive stress on hose reinforcement can create large holes between strands of hose reinforcement, and severely reduces the hose's pressure capacity. Exceeding the minimum bend radius can result in a burst hose. The minimum bend radii for each hose is stated in the hose tables in the catalog.
    
3. Avoid Twisting the Hose: Avoid placement that requires twisting the hose during installation, as it misaligns the reinforcement and reduces a hose’s capacity to withstand pressure. A simple way to identify twisting is to look at the layline, which is the continuous line of information printed on a hose with the part number, pressure, etc. If the layline is twisted like a candy cane, it means that the hose was twisted during installation, which can cause premature hose failure.
    
4. Use Elbow Fittings or Adapters When Necessary:  A general rule of thumb for hose installation is if the hose needs to bend immediately before the metal fitting, you should keep it straight for at least twice the outside diameter (O.D.). If that’s not possible, use a 90 or 45-degree elbow fitting. This prevents fluid under pressure, traveling at high speeds, from directly impacting the core tube, which can deteriorate the hose and cause premature failure. Adapters ease port connections and hose installation and can be used to change thread configuration. Adapters should be used sparingly to keep assembly components at a minimum to avoid longer assembly time and cost, and prevent potential leak points in hose assembly.
    
5. Avoid Abrasive Influences: Avoid placing hose near any object with sharp or abrasive surfaces, or too close to other hoses as direct surface contact with equipment components, hoses, or material in the operating environment will cause abrasive wearing of the outer cover, risking exposure of the reinforcement. However, if the application is such that contact cannot be avoided, either a hose with a higher abrasion resistant hose cover or a protective sleeve should be used. Parker ToughCover (TC) or SuperTough (ST) covers offer 80 times and 450 times respectively the abrasion resistance of standard rubber covers.
    
6. The Plane of Movement Must be Considered:  Be sure to route high-pressure hydraulic hose parallel to machine contours using elbows or adapters. This decreases the length of hose lines and reduces hard angle bends that restrict flow and strain the hose, saving money and maximizing hose capability.
    
7. Do Not Mix Hoses and Fittings: To ensure maximized service life and safe function, do not mix and match hoses and fittings from different manufacturers. It is vital to work capability and safety that the hose and fitting manufacturer are the same, and that the assembly uses the recommended equipment, parts, and procedures as per the manufacturer. Correct fittings can avoid unnecessary strain on the hose, excess length, or multiple threaded joints.
    
8. There is a Right and Wrong Way to Clamp Hoses:  Keep in mind the mechanical movement and vibration of hose when bundling. Crossing or clamping high- and low-pressure hoses together can lead to wear in the hose covers, decreasing productivity and risking safety hazards. Correct clamping should be exercised to securely route the hose and avoid the hose contacting surfaces that will cause the hose damage. If hose follows a compound bend, it should be coupled into separate segments or clamped into segments that flex on a single plane.
    
9. Temperature Directly Affects Hose Life: Keep hydraulic hoses away from external heat sources, as high ambient temperatures shorten hose life. Temperature increases of can lead to cracking and shorten hose life. The more extreme the ambient temperature is, weather hot or cold, the more durable the hose cover needs to be. Another option would be installing sleeves, which can help protect hose from hot equipment parts and other high temperature sources that are potentially hazardous.
    
10. Plan for Future Maintenance: Few things are more aggravating that having to take apart adjoining assemblies to access a specific hose that needs maintenance. Avoid this scenario by using different combinations of hose ends and tube fittings, such as short and long straights, or short and long elbows. Taking this step when installing a hose reduces maintenance effort and downtime. Avoid unnecessary hose strain by utilizing elbows and adapters for ease of routing. These tools help to relieve strain on the assembly and allow for clean, accessible installations. Inspection and maintenance might be necessary, so prohibitive design routings of hose assemblies should be avoided.

For more information about hose installation and routing, watch the video below or contact your Parker representative.

 

Article contributed by Kyri McDonough, marketing services manager at Hose Products Division, Parker Hannifin.

 

 

 

 

Other related topics on hydraulic hose, hose application, and selection criteria:

Top 5 Reasons Customers Choose GlobalCore Hose
Measure and Specify Hydraulic Hose Length With Ease
Decoding a Hydraulic Hose Layline
Top 8 Reasons Hydraulic Hoses Fail
Hydraulic Hose User Safety

Two things are equally important for reliable performance of an O-ring seal: the right size and the right material. Parker’s new O-Ring Selector is an engineering design tool that enables users to make the right material and size selections easily, quickly and reliably – in a single application. This post explains how to design the sealing system using the “Size Selector.”

See also blog post:

• O-Ring Selection Made Easy with the Parker O-Ring Selector
• How to Select the Right O-Ring Material with the Parker O-Ring Selector

 

 

Precise calculation of installation conditions: fast and easy with the “Size Selector”

The “Size Selector” calculates the installation conditions and the suitable O-ring. It is divided into three segments: “Hardware Configuration,” “Sizing Selection” and “Results” (of the calculation).

 

Description of the system to be sealed

The “Hardware Configuration” segment is used for a detailed description of the sealing system. The user can choose between two radial (Piston und Rod Seal) and two axial (Internal and External Pressure) sealing systems. Subsequently, these choices can be specified in greater detail by selecting liquid systems or gas/vacuum systems. The selection of the various options is intuitive due to the clear, graphic presentation of the individual sealing systems. 

“Hardware Configuration” also includes a look at the diverse thermal expansion coefficients of the hardware components. Representative values, e.g. for steel or aluminum, are available here. Of course, if known precisely, these values may also be entered manually to parameterize the sealing system with maximum accuracy. Chemical swelling of the seal itself may be included in the calculation as well.

 

 

 

 

 

 

 

  Calculation of the sealing system

The “Sizing Selection” segment is focused on the comprehensive calculation of the system to be sealed. If known, all values such as O-ring diameter, piston diameter, etc. can be entered manually. Alternatively – if complete information is not available – an automatic parameterization of the sealing system can be performed via the selection of the O-ring diameter and (for instance) the targeted piston diameter. All the individual values calculated this way can be adjusted manually in a second step and their effects on the functionality of the sealing system reviewed. The toleration of the hardware components can be adjusted to the user’s application as well to satisfy the various quality requirements in the manufacturing process.

 

 

 

 

 

 

 

 

 

 

 

 

Review of results

The “Results” segment displays the calculated results in a structured manner. For the key results parameters, the recommendations are shown according to ISO/Parker specifications. In addition, minimum and maximum tolerations for the results parameters are indicated. A simple visual check if the calculated sealing system corresponds to ISO/Parker recommendations is made using color codes: green stands for “Recommended,” yellow for “Warning” and red for “Critical.”  

Users can enter their own comments on the calculations made in “Notes.” After the review of the sealing system has been completed, the data obtained can be converted into a PDF.

 

 

 

 

 

 

 

 

>>> Start imperial version
>>> Start metric version

 

 

Additional information:

• O-Ring Selection Made Easy with the Parker O-Ring Selector
• How to Select the Right O-Ring Material with the Parker O-Ring Selector
• www.parker.com/o-ring-selector

 

 

Posted by:  

 

 

Dr. Heinz-Christian Rost
Technology & Innovation Manager
Engineered Materials Group Europe, Prädifa Technology Division

 

 

 

O-Ring Selection Made Easy with the Parker O-Ring Selector

How to Select the Right O-Ring Material with the Parker O-Ring Selector

 

 

Zwei Dinge sind für die zuverlässige Funktion einer O-Ring-Dichtung gleichermaßen wichtig: die richtige Größe und der richtige Werkstoff. Der neue O-Ring-Selector von Parker ist ein Konstruktions-Tool, das es dem Anwender ermöglicht, einfach, schnell und zuverlässig die geeignete Material- und Größenauswahl zu treffen – in einer einzigen Anwendung. In diesem Beitrag wird die Auslegung des Dichtsystems mit Hilfe des „Size Selectors“ erläutert.

Siehe auch Blog Posts

• O-Ring Auswahl leicht gemacht mit dem Parker O-Ring Selector
• O-Ring-Werkstoffauswahl mit dem Parker O-Ring Selector  

 

 

Einbausituationen präzise kalkuliert: einfach und schnell über den „Size Selector“

Im Bereich „Size Selector“ (Größenauswahl) erfolgt die Berechnung der Einbausituation und des geeigneten O-Rings. Dabei unterteilt sich der „Size Selector“ in drei Segmente. Die „Hardware Configuration“, die „Sizing Selection“ und die Ergebnisse der Berechnung („Results“):

 

Beschreibung des abzudichtenden Systems

Im Segment „Hardware Configuration“ erfolgt eine detaillierte Beschreibung des Dichtungssystems. Dabei kann zwischen zwei radial abdichtenden (Piston und Rod Seal) und zwei axial abdichtenden (Internal und External Pressure) Dichtungssystemen gewählt werden. Diese lassen sich dann jeweils weiter durch die Auswahl von Flüssigsystemen oder Gas-/Vakuumsystemen spezifizieren. Die Auswahl der verschiedenen Optionen ist aufgrund der klaren graphischen Darstellung der einzelnen Dichtungssysteme intuitiv.

Die „Hardware Configuration“ schließt auch die Betrachtung der unterschiedlichen thermischen Expansionskoeffizienten der Hardware-Komponenten mit ein. Hier kann auf repräsentative Werte beispielsweise für Stahl oder Aluminium zurückgegriffen werden. Bei genauer Kenntnis können die Werte aber natürlich auch manuell eingetragen werden, um eine möglichst genaue Parametrisierung des Dichtungssystems zu erreichen. Auch kann die chemische Quellung der Dichtung selbst in der Kalkulation berücksichtigt werden.

 

 

 

 

 

 

 

 

Berechnung des Dichtsystems

Das Segment „Sizing Selection“ konzentriert sich auf die umfassende Berechnung des abzudichtenden Systems. Wenn bekannt, können alle Werte wie O-Ring-Durchmesser, Kolbendurchmesser etc. manuell eingetragen werden. Es kann jedoch auch – bei  nicht vollumfänglicher Informationslage – über die Auswahl des O-Ring- Durchmessers und beispielsweise des angestrebten Kolbendurchmessers eine automatische Parametrisierung des Dichtungssystems durchgeführt werden. Alle so berechneten Einzelwerte können in einem zweiten Schritt manuell angepasst und die Auswirkung auf die Funktionsfähigkeit des Dichtungssystems betrachtet werden. Die Tolerierung der Hardware-Komponenten kann ebenso dem realen Fall angepasst und somit den unterschiedlichen Qualitätsanforderungen im Herstellungsprozess Rechnung getragen werden.

 

 

 

 

 

 

 

 

 

 

 

 

Ergebnisbetrachtung

Im Segment „Results“ werden die kalkulierten Ergebnisse strukturiert dargestellt. Für die wichtigsten Ergebnisparameter werden Empfehlungen (Recommendation) gemäß ISO-/Parker-Spezifikationen dargestellt. Weiterhin werden Minimal- und Maximal-Tolerierungen für die Ergebnisparameter angezeigt. Eine einfache visuelle Überprüfung, ob das kalkulierte Dichtungssystem den ISO- / Parker- Empfehlungen entspricht, erfolgt über eine entsprechende farbige Kennzeichnung: grün steht für „Empfehlung“ („Recommended“), gelb für „Warnung“ („Warning“), rot für „kritisch“ („Critical).

Eigene Kommentare zu den durchgeführten Kalkulationen können im Bereich „Notes“ erfasst werden. Ist die Betrachtung des Dichtungssystems abgeschlossen, können die ermittelten Daten in ein PDF konvertiert werden.

 

 

 

 

 

 

 

 

>>> Metrische Version starten
>>> Zöllige Version starten

 

 

Weitere Informationen:

Blig: O-Ring Auswahl leicht gemacht mit dem Parker O-Ring Selector

Blog: O-Ring-Werkstoffauswahl mit dem Parker O-Ring Selector  

www.parker.com/o-ring-selector

 

 

Ein Beitrag von

 

 

Dr. Heinz-Christian Rost
Technology & Innovation Manager
Prädifa Technology Division

 

 

O-Ring Auswahl leicht gemacht mit dem Parker O-Ring Selector

O-Ring-Werkstoffauswahl mit dem Parker O-Ring Selector

 

Inefficient energy allocation, heat generation and noise are typical concerns among facility engineers in manufacturing environments. Parker’s new variable speed drive solution, called Drive Controlled Pump (DCP), increases hydraulic power unit efficiency while maintaining high power density, precise control and performance. DCP is the pairing of electric motors, hydraulic pumps, electronic drives and software to meet the local load demands within your hydraulic system. Precisely controlled variable speed pump macros are custom configured to meet the functional requirements of each process within a complex hydraulic system. 

Here is a list of ten dos and don’ts when implementing DCP technology: 1. Right math matters.

Don’t just use the Hydraulic Power Equation to size the electric motor.

(HP = P x Q ÷ 1714)

Do compute the pump torque first, then use the motor’s base speed to compute power.

(T = Vi x P ÷ 24π)

(HP = T x N ÷ 5252). HP: Horse Power, P: Pressure PSI, Q: Flow GPM, T: Torque Ft-Lb, Vi: Pump Displacement In³/Rev, N: motor base speed (4 pole motor’s base speed = 1,800 RPM).

  2. Pump losses matter.

Don’t just use load’s flow and pressure demand to compute motor power.
Do consider the pump’s internal flow and torque losses at various speeds and pressures.

  3. Power to accelerate flow matters.

Don’t be content with power computations to maintain flow and pressure.
Do allow for the acceleration power requirement. Variable speed pump controls need reserved power to accelerate the combination of the electric motor rotor, couplings and the pump’s rotating group while under full pressure. The reserved power gets larger with the acceleration rate and rotor moment of inertia.

Ta = I x Δω / (308 x Δt), Ta: Acceleration Torque(Ft-Lb), I moment of inertia (LB-Ft2), Δω: Speed Change (RPM), Δt: Speed Change (Sec)

4. Exact motor size matters.

Don’t oversize the electric motor. Oversized motors have larger rotor inertia and require larger drives to power.
Do break down the cycle by pressure, flow and time. Compute each segment for power.

  5. Maximum pressure and flow matters.

Don’t just use maximum flow and maximum pressure to compute power. You might end up with an oversized motor.
Do use the larger of the two computed horsepower values. Compare flow at maximum pressure and pressure at maximum flow.

  6. Hydraulic peak power matters.

Don’t just use the RMS value of computed power segments to size the electric motor.
Do use the RMS value, yet pay attention to peak power. Peak power should be less than 150% of the selected motor size, and its duty cycle must be within the operation parameters of the electric motor and drive.

  7. Electric motor frame size matters.

Don’t use your standard TENV electric motor for variable speed fixed pumps.
Do use low rotor inertia motors to minimize reserve acceleration power. Open frame and force ventilated motors offer much lower rotor inertia.

  8. Electric motor base speed matters.

Don’t exceed the induction motor’s base frequency when operating at maximum pressure.
Do exceed motor’s base frequency only when pressure drops proportional to over-speed.

  9. Pump minimum speed matters.

Don’t operate below the minimum recommended pump speed. Operating below minimum speed damages the pump.
Do add a controlled bleed off loop to the pump’s outlet to limit its minimum speed. Also, an accumulator can allow the pump to get turned off at deadhead conditions.

  10. Flow change rate matters.

Don’t accelerate/decelerate a pump too fast.
Do limit the pump speed change rate to stay above the pump’s minimum inlet pressure to avoid cavitation. Also, keep in mind rapid pump speed changes consume additional power which can lower the HPU’s efficiency.

To learn more about Drive Controlled Pump (DCP) Technology, download the white paper, Integrated Energy-Saving Hydraulic Systems Customized to Your Application Requirements here or view the on-demand presentation.

 

Rashid S. Aidun who draws on his electrical and fluid power background to create custom drive controlled pump solutions. Prior to joining Parker 17 years ago, he worked as an industrial manufacturing and fluid power and controls engineer for various OEMs. He has a BSME from Syracuse University.

 

 

 

 

 

Improve Steel Coiling Process Efficiency With DCP

Energy-Saving Hydraulic Systems Using Drive Controlled Pump (DCP)

 

 

 

 

 

There are numerous manufacturers in the water cooler market. Water coolers are also called chillers but it is important to draw a clear distinction between process water coolers and chillers for industrial or non-industrial cooling applications.

Many people think that all chillers for the industrial manufacturing sector are the same but there is a risk of making a huge error of judgment which could have an impact on the final choice for the application.

 

Chiller market

 

When referring to cooling and climate control systems, we mean systems that can control both the temperature and the humidity level of a space. They are usually used for cooling rooms, electrical cabinets or other places where the water cooling temperature does not have to be precise and constant.

Chillers for cooling process water, on the other hand, are compression water cooling units that can be sub-divided, depending on the fluid used for the cooling of the condenser, into air-cooled and water-cooled. The most common cooling power range for installed systems is between 2 and 750 kW.

Process coolers for industry provide a high and constant degree of precision of the output water temperature (in all atmospheric conditions) and keep the fluid clean to prevent damage to the end user. In fact, process chillers are used to cool industrial machinery that requires the cooling fluid to be uncontaminated and at a precise and constant temperature. For example, in all of the hydraulic circuits of machines, if the oil temperature exceeds a certain limit, the machine shuts down with a resulting loss of productivity. Therefore, precise and constant cooling is both necessary and crucial for speeding up and improving production processes. When there is a need for accuracy and a water temperature lower than the ambient temperature, precision process coolers offer the only solution. A precision cooling chiller is a machine designed to cool water using a cooling circuit. It is a closed circuit which must ensure:

• No waste of the cooling fluid.
• No control of outlets.
• Control of the water quality.
• Modularity: possibility for expansion.
• Complete flexibility.
• Water temperature can be set.
• Independence from ambient conditions.

  Applications requiring cooling capacities from 2kW to 24kW

Parker's Hyperchill Plus industrial water chiller is compact, easy to use, safe and reliable in all operating conditions — guaranteeing precise and accurate control of the water temperature. Cooling capacities range from 1.7kW to 23.6kW. The availability of a wide range of accessories and options makes Hyperchill Plus an extremely flexible solution which can satisfy demands in all industrial applications. Thanks to the non-ferrous hydraulic circuit, Hyperchill Plus ensures stable operating conditions, maintaining the highest possible quality and cleanliness, which has an ensuing positive impact on the efficiency and productivity of the process, reducing maintenance costs and system downtime. Each individual Hyperchill Plus is extensively tested in the factory to guarantee the highest possible levels of efficiency and reliability in all operating conditions.

 

Applications requiring cooling capacities from 28kW to 360kW

Parker's Hyperchill range of water chillers is designed specifically for industrial applications. Advanced solutions, the utmost attention to detail and a highly sophisticated production process have resulted in a compact, reliable and easy-to-use product that offers flexibility in a variety of conditions as well as precise control of the water temperature. The high level of efficiency and low operating costs make Hyperchill the perfect solution for the modern industry.

Parker is the leading supplier of water coolers for production processes which offer complete ease of use and a high degree of operational reliability thanks to the use of the latest technologies and the availability of a vast array of versions and accessories. The Parker liquid coolers range represents a simple but effective solution to most common problems arising from the use of water. The chart below contains general technical specifications.

 

 

To learn more about Hyperchill Plus download the brochure. 

 

 

 

 

 

 

For information on Parker's complete compressed air and gas treatment solutions including the Hyperchill range of water chillers, download the brochure.

 

 

 

 

 

 

This article was contributed by Fabio Bruno, compressed air purification, gas generation & process cooling application engineer, Parker Gas Separation and Filtration Division EMEA.

 

        Related content

Sizing a Chiller for Your Application - What You Need to Know 

Why You Need a Maintenance Plan for Manufacturing Equipment

Protect Your Process from Mycoplasma Contamination

Filtration Technologies and Key Markets

 

 

 

 

A large percentage of compressor failures in low-temperature vapor-compression refrigeration system applications originate from overheating. Typical compressor capacity rating data is based on an industry standard of a 65°F return vapor temperature. While a 65° return vapor temperature may be satisfactory for high-temperature applications and, perhaps, some medium-temperature applications, unsatisfactorily high-discharge temperatures are virtually unavoidable on low-temperature applications. This is due, in large part, to the thermodynamic properties of the refrigerant.

Refrigeration oils have been highly refined in an effort to elevate the temperature at which chemical decomposition occurs, and experience has shown mineral oil decomposition begins when compressor internal temperatures reach 350°. Compressor manufacturers typically indicate that discharge gas temperatures are 50° to 75° higher at the discharge valve inside the compressor than out on the discharge line, 6-8 inches from the service valve. Therefore, dangerously high temperatures already exist inside the compressor when discharge line temperatures are well below 350°. This lubricant decomposition is accelerated by residual contaminants that are present in a typical system. Studies have shown the rate of chemical reaction doubles with every 18° temperature increase. For example, a chemical reaction that takes 10 years to complete at 100° will only take five years to complete at 118°. At 136°, it would be completed in two-and-a-half years.

However, mineral oils are vulnerable to losing the lubrication film necessary to prevent metal-to-metal contact between bearings and journals, or piston rings and cylinders, prior to the temperature at which decomposition begins. With mineral oil, this occurs approximately between 310° and 330°. When these compressors’ internal temperatures are reached, the probability of extreme piston and ring wear is imminent.

Refrigerant evolution

Hydrocarbons (HCs) and other natural refrigerants were employed in early vapor-compression refrigeration application designs. Many of these were highly flammable, toxic, or both. Developments in the late 1920s and into the early 1930s delivered a small group of organic compounds — the chlorofluoocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) for use as refrigerants — and CFCs and HCFCs proliferated into all types of refrigeration and comfort cooling applications. This continued unimpeded for nearly 50 years. These refrigerants typically were selected for various applications in large part based on their favorable thermodynamic properties relative to the system type in which they were to be applied. That is, CFC-12 was predominantly used for medium-temperature refrigeration, CFC-502 was predominantly used for low-temperature refrigeration, and HCFC-22 was principally used for comfort cooling.

However, in the late 1970s, environmental concerns with CFCs and HCFCs arose owing to scientific theories linking these organic compounds to concerns of global ozone depletion. Chorine-containing CFCs were quickly targeted for elimination from use as refrigerants. HCFCs, which contained a smaller amount of chlorine, also were earmarked for eventual elimination.

To speed the move away from CFCs, HCFC-22 initially was more widely specified for new and retrofit use in both medium- and low-temperature refrigeration systems. Additionally, a number of zeotropic blend refrigerants containing predominantly HCFC-22 appeared on the scene and were deployed as interim replacements for CFC compounds.

Prior to this, HCFC-22 had already been in wide use in systems with higher saturated suction temperatures for comfort cooling. However, the extended use of HCFC-22 into medium- and low-temperature refrigeration applications was not without its challenges.

Because of the thermodynamic properties of HCFC-22 — which result in decreased vapor density and increased compression ratios — lower saturated suction temperatures clearly would result in unsatisfactorily high discharge temperatures and the associated oil decomposition and lubrication problems without further intervention.

Consequently, as HCFC-22 was considered to replace CFC refrigerants in medium- and low-temperature refrigeration applications, a need was quickly recognized to address these inherent high-discharge temperatures to ensure a reasonable life expectancy of compressors.

Compound compression techniques were implemented to combat high compression ratios, and liquid injection methods, including the use of desuperheating thermostatic expansion valves (TEVs) to address high discharge temperatures, were adopted for new equipment installations.

Applying the TREV

One cost-effective method of preventing destructive superheat at the compressor for these HCFC-22 medium- and low-temperature systems was the introduction of the temperature responsive expansion valve (TREV). Using liquid from the high side of the system, the TREV injects saturated refrigerant into the suction line ahead of the compressor in direct response to the temperature of the discharge line.

This valve does not have an equalizer line and is not influenced by system pressure as a desuperheating TEV is. A sensing bulb is placed on the compressor discharge line 6 inches from the compressor discharge outlet connection. The valve responds directly to a rise in discharge gas temperature. Temperature settings are available from 115° through 275°. A bellows assembly similar to that employed in a direct-acting pressure regulating valve is used. The valve power element is charged with a hydraulic fluid that expands as its temperature increases. Multiple capacity sizes are offered for HCFC-22 to a nominal capacity maximum of 5 ton (see Table 1 below).

A liquid supply line to the TREV is connected to a high side location that will provide vapor-free liquid to the valve inlet. The TREV is designed to feed saturated refrigerant directly into the compressor suction line 12-18 inches before the compressor. Other locations are possible, and the suitability of these locations should be determined by proper testing and evaluation. Good thermal contact between the sensing bulb and the discharge line is essential, and insulating the bulb with a high-temperature insulation, such as fiberglass or its equivalent, is recommended.

 

From the onset of the more extensive use of HCFC-22 to replace CFCs in medium- and low-temperature systems, it was recognized that eventually it, too, would be eliminated from use. Chemical companies conducted ongoing research and development to offer suitable long-term substitute refrigerant compounds, and hydrofluorocarbon (HFC) refrigerants with zero ozone-depletion potential were developed. HFC-404A and -507 quickly became the commonly specified refrigerants for medium- and low-temperature refrigeration systems.

HFC-404A and -507 were considered “cooler” refrigerants by comparison to HCFC-22 regarding discharge temperature. However, even with these HFC refrigerants, destructive superheat caused by higher condensing temperatures has been experienced periodically in some geographical areas of the U.S. during operation in peak summer conditions, specifically in low-temperature applications. Liquid injection has continued to be employed but with less frequency.

Design advances 

As compressor designs evolved, an inherent reduction in compressor temperatures was achieved on specific applications. These design improvements fall into several areas, such as reduced contact between the motor and compressor housing, improved motor designs, reduced volumetric clearances due to improved machining tolerances, and minimization of heat transfer between the high- and low-pressure areas of the compressor.

Meanwhile, the international scientific community initiated concern over global warming. Concerns about greenhouse gases enter the worldwide consciousness, and chemical compounds were evaluated for their global warming potential (GWP). This led to the introduction of HFC refrigerants with comparable thermodynamic properties but lower GWPs than HFC-404A and -507 for medium- and low-temperature applications. HFC blend refrigerants designated as HFC-407A and -407F were developed. Compared to HFC-404A, (GWP = 3,922), HFC-407A (GWP = 2,107) offers a reduction of just less than 50 percent and HFC-407F (GWP = 1,824) provides a reduction of just more than 50 percent in GWP. Of these two refrigerants, HFC-407F exceeds in capacity and efficiency. However, discharge temperatures for HFC-407F are greater by comparison than that of HFC-404A and -507.

Once again, a means of reducing discharge temperatures to maintain quality of lubricant and extended compressor life was desired. Liquid injection using the TREV, while having been developed originally to address high discharge temperatures associated with HCFC-22 use on low-temperature applications, has proven to be a suitable device for application with HFC-407F as well. Because it is a temperature-responsive valve, which is not impacted by system pressures, this liquid injection valve may be satisfactorily applied in HFC-407F applications to eliminate potential lubricant decomposition due to high-discharge temperature operation. And, it can be field-applied as needed to existing systems as they are converted from a previously specified refrigerant to HFC-407F.

TREVs and the future

The chemical companies continue to pursue safe, low-GWP refrigerants while maintaining suitable performance characteristics to replace those that have gone before. The most recently introduced low-GWP refrigerant alternatives are hydrofluoroolefin (HFO) compounds. Pure HFO refrigerants have GWP numbers below 1, meaning they are of less concern regarding global warming than even carbon dioxide. They are safety-classified as A2L by ASHRAE (nontoxic but mildly flammable); however, it was discovered that by blending HFOs with HFCs, the mild flammability is mitigated, resulting in an ASHRAE classification of A1 (nontoxic and nonflammable) although with an increase in the GWP number.

These HFO/HFC blend refrigerants are entering the marketplace. They are considered as chemically safe, similarly performing refrigerant alternatives with a markedly lower GWP than HFC-404A and -507. HFO/HFC-448A and HFO/HFC-449A are proving to be very suitable alternatives to continue the transition away from HCFC-22. Additionally, they are also considered useful substitutes for the higher-GWP HFC-404A and -507.

In the evaluation of HFO/HFC-448A and HFO/HFC-449A, it has been recognized that, once again, dangerously high discharge temperatures and the associated probability of lubricant decomposition may be unavoidable, particularly on low-temperature systems. Thankfully, the TREV continues to be available as an effective component that may be deployed to allow systems to operate at acceptable compressor discharge temperatures with these new blended refrigerant compounds.

The TREV, as a true temperature responsive valve that is not influenced by system pressures, continues to be an effective problem-solving tool for new alternative refrigerants that may experience potentially destructive high compressor discharge temperatures. It will also more than likely continue in this role as the refrigerant landscape continues to unfold.

 

HVACR Tech Tip Article contributed by Gene Ziegler, technical training manager, Sporlan Division of Parker Hannifin

 

 

 

 

Additional resources on HVACR Tech Tips:

HVACR Tech Tip: Guide to Servicing Blended Refrigerants

HVACR Tech Tip: When Should a Catch-All Filter-Drier be Changed?

HVACR Tech Tip: Obtaining Oil Samples in a Refrigeration or Air Conditioning System