why is my hydraulic pump overheating factory

Hydraulic pumps generate heat while they run. However, hydraulic fluid temperature should never exceed180 degreesF (82 degrees C) under normal working conditions. If your hydraulic pump temperature rises above this, then that is a sign that your pump is likely overheating. One of the most common causes of hydraulic system failure is a hydraulic pump that runs too hot or overheats.

When a hydraulic pump runs at a too-high temperature for too long, it can ultimately lead to pump failure. Once a hydraulic pump begins to fail, it can potentially damage the entire hydraulic system by sending contaminants and debris into the system that can damage its other components.

In addition, when some hydraulic fluids are subject to high temperatures, they can thin and lose their viscosity. When hydraulic fluid is too thin, it is much more likely to leak, and fluid that has lost its viscosity cannot lubricate your pump properly. Extremely hot fluid can also damage pump seals, further increasing the chance of a pump leak.

Some hydraulic fluids thicken and oxidize when exposed to high heat instead of thinning. When hydraulic fluids are too thick, they can restrict flow throughout the entire hydraulic system, which leads to your system heating up even further.

The sooner you determine why your hydraulic pump is running hot and repair the cause of the problem, the less likely your hydraulic system will develop irreversible damage or fail completely.

Hydraulic pumps overheat for many reasons. Just a few of the most common causes of hydraulic pump overheating include: Contaminated hydraulic fluid. When fluid has debris and dirt, contaminant particles can quickly build up on hydraulic system filters, leading to filter clogs. Your pump has to work harder to pump fluid through clogged filters, which leads to overheating.

Aeration. Air leaks at seals and fittings on your hydraulic system components can lead to air entering your system and forming bubbles in your fluid. Air bubbles generate heat when your system compresses them and then pass this heat into the surrounding fluid, overheating it.

Low reservoir fluid. Since your hydraulic system releases some of the heat it creates into reservoir fluid, a low reservoir fluid level can contribute to overheating.

Blocked or damaged heat exchanger. This component is also an important part of your hydraulic pump"s cooling system. If it is blocked or damaged, then it cannot help remove heat from your pump properly.

Once your hydraulic pump beings overheating, you need to find the cause of the problem and repair it. That way, your pump can begin operating within its ideal temperature range again.

If your pump overheats due to fluid contamination, then either remove all contaminants from existing fluid or remove the current contaminated fluid from the system and add fresh fluid. Be sure to filter all fresh hydraulic fluid before you add it to your system because even this fresh fluid can contain contaminants. Also, replace your fluid filters on a regular basis to prevent the overheating that can occur when these filters become blocked with debris.

If air has entered your system through leaky seals and fittings, then have a hydraulic system repair expert inspect and replace or tighten these fittings. Have a hydraulic system repair expert also look at heat exchanger damage to determine if the exchanger needs repairing or replacing.

Finally, be sure to check your system"s reservoir fluid level on a regular basis. Add new fluid when necessary to help this reservoir perform its important task of helping to keep your pump cool.

Your hydraulic pump should always operate within its ideal temperature range. If your pump is running hot, then contact the hydraulic pump experts at Quad Fluid Dynamics, Inc., forhydraulic pump diagnosis and repairtoday.

Is your hydraulic pump getting excessively hot during normal operation? Pumps do generate heat when running, however they are designed with specific heat parameters in mind. Overheating is an abnormal condition that leads to destructive issues such as thinning of hydraulic fluid, which leads to reduced lubrication, metal-on-metal contact of moving parts. And accelerated pump wear and failure.

Therefore it is never a good idea to ignore a pump that is exceeding its heat parameters under normal load. There are a number of factors that contribute to an excess buildup of heat and in this article, we’ll explain some of these issues.

Hydraulic fluid viscosity refers to the thickness or “resistance to pouring” of your hydraulic fluid. This is very important to the correct operation of your pump. The fluid not only transmits the power that moves your drives and actuators. It also lubricates internal components and removes heat from the system. Hydraulic fluid is designed to operate at a specific temperature range. As it heats, it becomes thinner and eventually it will lose the ability to lubricate moving parts. The increased friction may cause the pump to heat up, and naturally increased wear will be taking place when this is happening. On the other hand, hydraulic fluid that is too thick flows less efficiently within the system, which also results in heat buildup.

Fluid that is contaminated with dirt, debris, water and other impurities may cause heat build up in a few ways. Blocked fluid filters, pipes and strainers place undue load on the pump or even lead to pressure drops on the back side of filters that cause cavitation.

Low fluid levels can result in a condition in which not enough flow is reaching the critical hydraulic components and moving parts. This is known as oil starvation and just like running your car without oil, it will increase metal-on-metal friction and lead to increased heat and wear. Oil starvation can also be caused by clogged hydraulic filters, incorrect fluid reservoir design.

Cavitation is the rapid formation and implosion of air cavities in the hydraulic fluid. When these air cavities collapse under pressure, they generate a lot of heat. In fact, temperatures can reach up to 2700 degrees C at the point of implosion! Not only does cavitation compromise the lubrication properties of the oil, the excessive heat that is generated is extremely damaging to the hydraulic pump and the system as a whole. Attacking hoses and seals and causing metal components to expand and wear.

This happens when air makes its way into the system via air leaks at points like pump seals, and pipe fittings. And what happens next in a hydraulic system? Compression! Air generates heat when compressed, which naturally leads to an increase in temperature if left untreated. In extreme circumstances it can also lead to ‘hydraulic dieseling’ whereby compressed air bubbles actually explode in the same process that powers diesel engines. This is not good and leads to degradation of the fluid and damage to system components through loss of lubrication and burning of seals.

As pumps wear, the internal leakage or “slippage” increases. Essentially, fluid is able to make its way past tight fitting components, which reduces the efficiency of the pump, but in addition, as this occurs, fluid moves from a high pressure to a low pressure without doing any mechanical work, since according to the laws of physics energy cannot be destroyed, it is instead converted into heat.

A build-up of excessive heat is a symptom of hydraulic pump problems, but it is far from the only signal that there may be something wrong. There are other important warning signs that you should pay attention to. These include unusual noises, pressure problems and flow problems. Each of these symptoms provide clues about any potential pump problems that need to be addressed - so it’s important to familiarise yourself with all of these issues. To help, we’ve created a downloadable troubleshooting guide containing more information about each of these issues. So that you can keep your system up and running and avoid unplanned downtime. Download ithere.

Overheating isa frequent problemwithin hydraulic systems that may be determined by specific components. Thisinternal problem lies within the pump and causes a hydraulic system to overheat in the following ways:

Contaminated hydraulic fluid is a common cause for a Hydraulic system to overheat. This can occur when the container is not sealed properly which causes dust, dirt,debris,or moisture to contaminate the fluid.With hydraulic systems running at higher pressures and more efficiently than ever before, it is important tomonitorthe cleanliness of one’s hydraulic fluid. Reducing contamination can decrease damage andwillallowoneto get the most out oftheirequipment.

Wrong valve calibration could resultin pressure difficulties which can cause a hydraulic system to overheat. The main cause of this is when a facility’s plant design changes and maintenance recalibrate the pressure relief valves for the updated operating pressure. If maintenance adjusts the pressure,and it stilldoes notsolve the problem, the pressure relief valve may have to be replaced entirely. Erosion to a valve is a common occurrence as dirt and debris settle and collectthroughout time. Maintaining the correct pressure will help your system keep up with production and not slow down.

Aeration in a hydraulic system can bea common issueand is caused by an outside air leak in the suction line.The pressure used in the suction line of hydraulic systems is below atmospheric pressure, so oilcannotleak out, but air can leak in.This will occur when there are loose, leaky seals and fittings which will allowtheair to seep in.Aeration can have severalnegative effectson top of overheatingsuch as increasedpump cavitation, excessive noise, and loss of horsepower.Some symptoms of Aeration may include foaming of the fluid, irregular movements, and banging and or loud clicking noises as the hydraulic system compresses and decompresses.

A blocked heat exchanger is significant toheating one’s hydraulic system, while cooling it down is just as important.Aninfrared thermometer isan effective wayto checkthe temperatureof a heat exchanger. Theadjustments can be made according tothedesign of theflow rateof oil.Make sure to replace the fluid fitterslocatedin the pumpon a regular basis to ensure theywill not get blocked andoverheat.

Oil Type plays a critical role inany hydraulic system. The wrong oil will not only affect the performance of the system but also cut down the lifespan of the machine. Theoil Viscositydeterminesthe maximum and minimum temperatures in which a hydraulic system can safelyoperate.Thin oils have a lowviscosity andflow more easily at low temperaturesthanthicker oils that have a higherviscosity.If the oil is too thin it can cause internal friction whichcreates heat and cancausethe system to overheat.

Low reservoir fluid is a common cause ofoverheating in hydraulic systems as itreleasesbuilt-upheatfrom the machineintothe fluid. Not having enough reservoir fluid cancontribute tocavitation andultimate damage to the pump.

Hydraulic pump failure candamage the entire hydraulic system.When a pump fails,debris, dirt, and grime kick out downstreamand can affect theoil,filter,valves, fluid, and actuator.Contactour KICK@$$ hydraulic system repair professionalsat Allied Hydraulic to avoid these problems.

Overheating ranks No. 2 in the list of most common problems with hydraulic equipment. Unlike leaks, which rank No. 1, the causes of overheating and its remedies are often not well understood by maintenance personnel

Heating of hydraulic fluid in operation is caused by inefficiencies. Inefficiencies result in losses of input power, which are converted to heat. A hydraulic system’s heat load is equal to the total power lost (PL) through inefficiencies and can be expressed as:

If the total input power lost to heat is greater than the heat dissipated, the hydraulic system will eventually overheat. Installed cooling capacity typically ranges between 25 and 40 percent of input power, depending on the type of hydraulic system.

How hot is too hot? Hydraulic fluid temperatures above 180°F (82°C) damage most seal compounds and accelerate degradation of the oil. While the operation of any hydraulic system at temperatures above 180°F should be avoided, fluid temperature is too high when viscosity falls below the optimum value for the hydraulic system’s components. This can occur well below 180°F, depending on the fluid’s viscosity grade.

To achieve stable fluid temperature, a hydraulic system’s capacity to dissipate heat must exceed its heat load. For example, a system with continuous input power of 100 kW and an efficiency of 80 percent needs to be capable of dissipating a heat load of at least 20 kW. Assuming this system has a designed cooling capacity of 25 kW, anything that increases heat load above 25 kW or reduces the cooling system’s capacity below 25 kW will cause the system to overheat.

Consider this example. I was recently asked to investigate and solve an overheating problem in a mobile application. The hydraulic system was comprised of a diesel-hydraulic power unit, which was being used to power a pipe-cutting saw. The saw was designed for sub-sea use and was connected to the hydraulic power unit on the surface via a 710-foot umbilical. The operating requirements for the saw were 24 GPM at 3,000 PSI.

The hydraulic power unit had a continuous power rating of 37 kW and was fitted with an air-blast heat exchanger. The exchanger was capable of dissipating 10 kW of heat under ambient conditions or 27 percent of available input power (10/37 x 100 = 27). The performance of all cooling circuit components were checked and found to be operating within design limits.

At this point it, was clear that the overheating problem was being caused by excessive heat load. Concerned about the length of the umbilical, I calculated its pressure drop. The theoretical pressure drop across 710 feet of ¾-inch pressure hose at 24 GPM is 800 PSI. The pressure drop across the same length of 1-inch return hose is 200 PSI. The theoretical heat load produced by the pressure drop across the umbilical of 1,000 PSI (800 + 200 = 1,000) was 10.35 kW. This meant that the heat load of the umbilical was 0.35 kW more than the heat dissipation capacity of the hydraulic system’s heat exchanger. This, when combined with the system’s normal heat load (inefficiencies) was causing the hydraulic system to overheat.

Hydraulic systems dissipate heat through the reservoir. Therefore, check the reservoir fluid level and if low, fill to the correct level. Check that there are no obstructions to airflow around the reservoir, such as a buildup of dirt or debris.

Inspect the heat exchanger and ensure that the core is not blocked. The ability of the heat exchanger to dissipate heat is dependent on the flow-rate and temperature of both the hydraulic fluid and the cooling air or water circulating through the exchanger. Check the performance of all cooling circuit components and replace as necessary.

An infrared thermometer can be used to check the performance of a heat exchanger, provided the design flow-rate of hydraulic fluid through the exchanger is known. To do this, measure the temperature of the oil entering and exiting the exchanger and substitute the values in the following formula:

For example, if the measured temperature drop across the exchanger is 4ºC and the design oil flow-rate is 90 L/min, the exchanger is dissipating 10 kW of heat. Relating this to a system with a continuous input power of 100 kW, the exchanger is dissipating 10 percent of input power. If the system is overheating, it means that either there is a problem in the cooling circuit or the capacity of the exchanger is insufficient for the ambient operating conditions.

On the other hand, if the measured temperature drop across the exchanger is 10ºC and the design oil flow-rate is 90 L/min, the exchanger is dissipating 26 kW of heat. Relating this to a system with a continuous input power of 100 kW, the exchanger is dissipating 26 percent of input power. If the system is overheating, this means that the efficiency of the system has fallen below 74 percent.

Where there is a pressure drop, heat is generated. This means that any component in the system that has abnormal, internal leakage will increase the heat load on the system and can cause the system to overheat. This could be anything from a cylinder that is leaking high-pressure fluid past its piston seal, to an incorrectly adjusted relief valve. Identify and change-out any heat-generating components.

A common cause of heat generation in closed center circuits is the setting of relief valves below, or too close to, the pressure setting of the variable-displacement pump’s pressure compensator. This prevents system pressure from reaching the setting of the pressure compensator. Instead of pump displacement reducing to zero, the pump continues to produce flow, which passes over the relief valve, generating heat. To prevent this problem in closed center circuits, the pressure setting of the relief valve(s) should be 250 PSI above the pressure setting of the pump’s pressure compensator (Figure 1).

Continuing to operate a hydraulic system when the fluid is over-temperature is similar to operating an internal combustion engine with high coolant temperature. Damage is guaranteed. Therefore, whenever a hydraulic system starts to overheat, shut it down, identify the cause and fix it.

You can use multiple different upgrades and tuning methods on hydraulic systems. Many users will invest in upgrades that promise more flow and speed. The issue with these upgrades is that they"re not always fit for the hydraulic systems they"re applied to.

Since everything needs to stay in balance, you must make sure your upgrades match the entirety of your hydraulic system. For example, a higher flow pump can help give increased capabilities to a hydraulic system, but did you also check to see if the system"s hoses and piping can handle that increase in flow?

The increased flow can hit your smaller hoses hard and require more pressure just to get through them. This goes for any part of the hydraulic system that isn"t readily capable of handling more flow.

When you make upgrades, also ascertain if you need to change other components. In the example of the higher flow pump, you can simply increase your hose size, and that makes all the difference.

Whether you have a welded rod cylinder or telescopic cylinder, chances are you already know how destructive cylinder issues like fluid leaks can be. While leaks are known to cause cylinder issues, system overheating can be less obvious but just as pervasive. Hydraulic system overheating problems can be caused by different factors, including high heat hydraulic oil temperatures as well as system design pressure issues.

Hydraulic system heat contamination issues can be caused by different factors. With heat loading issues occurring from different sources, it is important to determine the correct cause of overheating for your hydraulic system. Common causes of hydraulic system overheating include:

Hydraulic fluid temperatures should stay within operating norms. Elevated or hot hydraulic oil can increase the chance of a system breakdown. High heat on hydraulic oil can increase oxidation, decreasing the oil’s performance and ability to maintain proper temperatures.

Higher hydraulic fluid temperatures can also create low viscosity issues. Maintaining normal viscosity levels allows your hydraulic system to function without added concerns about pump and valve wear and damage due to low viscosity.

Lack of fluid flow throughout your hydraulic system can cause motor issues as well as pump malfunctions and failure. Damage to your motor or pumps can require repair or component replacement.

Pressure issues can cause lack of fluid flow through your system. Pressure drop can occur due to lack of fluid flow through your system, resulting in higher operating temperatures and overheating.

While system damage from heat load can occur at any time, there are ways you can reduce and minimize system overheating. Troubleshooting tips for preventing hydraulic system overheating include:

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Remember that hydraulic system running at 145 F last fall? The one you didn’t worry about with cooler weather on the way? In the middle of summer, it could be operating even hotter—if it hasn’t already shut down. That’s because any industrial hydraulic system that runs higher than 140 F is too hot. The resulting problems are costly:

Fluid power specialist Al Smiley of GPM Hydraulic Consulting, Monroe, GA, has dealt with countless hydraulic systems in industrial operations throughout the past 20 years. We asked him for ways to troubleshoot hot-running systems.

“First things first,” said Smiley, “it’s important to keep in mind that all hydraulic systems generate a certain amount of heat.” Approximately 25% of the input electrical horsepower will be used to overcome heat losses in a system. Whenever oil is ported back to the reservoir, and no useful work is done, heat will be generated.

The tolerances inside pumps and valves normally permit a small amount of oil to continuously bypass a system’s internal components, causing the fluid temperature to rise. When oil flows through the lines, several resistance points are encountered. For example, flow-control, proportional, and servo valves control the flow by restricting it. When oil flows through those valves, a pressure drop occurs. This means a higher pressure will exist at the inlet port than at the outlet port. Any time oil flows from a higher to a lower pressure, heat is generated and absorbed in the oil.

When a hydraulic system is designed, the reservoir and heat exchangers are sized to remove that heat—some of which is allowed to dissipate through the reservoir walls to the atmosphere. “Heat exchangers, if properly sized,” Smiley noted, “should remove the balance of the heat and allow the system to operate at approximately 120 F.”

Fig. 1. Pressure-compensating piston pumps are the most common type used in industrial hydraulic systems. The tolerances between the pistons and barrel are approximately 0.0004 in.

The pressure-compensating piston pump (Fig. 1) is the most commonly used type in industrial hydraulic systems. Tolerances between the pistons and barrel are approximately 0.0004 in. A small amount of oil at the pump outlet port will bypass through these tolerances, flow into the pump case, and then be ported back to the reservoir through the case-drain line. “This case-drain flow,” noted Smiley, “does no useful work and is, therefore, converted into heat.”

According to Smiley, the normal flow rate out of the case-drain line is 1% to 3% of the maximum pump volume. For example, a 30-gpm pump should have approximately 0.3 to 0.9 gpm of oil returning to the tank through the case drain. “A severe increase in this flow rate,” he explained, “will cause the oil temperature to rise considerably.”

To check the flow rate, the line can be ported into a container of known size and the flow timed “unless personnel have verified that the pressure in the hose is near zero psi,” Smiley warned, “they should not hold the line during this test.” The line should, instead, be secured to the container, he advised.

A flow meter can also be permanently installed in the case-drain line to monitor flow rates. Check it regularly to determine the amount of bypassing. The pump should be changed when the oil flow reaches 10% of the pump volume.

Fig. 2 (top). During normal operation of this typical variable-displacement, pressure-compensating pump, when system pressure is below the compensator setting (1,200 psi), the internal swash plate is held at maximum angle by the spring. This arrangement allows the pistons to fully stroke in and out, permitting the pump to deliver maximum volume. Flow from the outlet port of the pump is blocked through the compensator spool.

Fig. 3 (bottom). Once the pressure builds to 1,200 psi, the compensator spool shifts, directing oil to the internal cylinder. As the cylinder extends the angle of the swash plate, it moves to a near-vertical position. At this point, the pump will only deliver enough oil to maintain the 1,200-psi spring setting. The only heat generated by the pump at this time is from the oil flowing past the pistons and through the case-drain line.

Figure 2 is a diagram of a typical variable-displacement pressure-compensating pump. During normal operation, when the system pressure is below the compensator setting (1,200 psi), the internal swash plate is held at maximum angle by the spring. This allows the pistons to fully stroke in and out and let the pump deliver maximum volume. Flow from the pump’s outlet port is blocked through the compensator spool.

Figure 3 shows the condition of the same pump when pressure reaches 1,200 psi, and the compensator spool shifts, directing oil to the internal cylinder. As the cylinder extends the angle of the swash plate, it moves to a near-vertical position. At that point, the pump will only deliver enough oil to maintain the 1,200-psi spring setting. “The only heat generated by the pump at this time,” Smiley noted, “is from the oil flowing past the pistons and through the case-drain line.”

Fig. 4. Many pressure-compensating pumps incorporate a relief valve as a safety backup in case the compensator spool sticks in the closed position. The relief valve should be set 250 psi above the pressure-compensator setting. Since the relief-valve setting is above that of the compensator, no oil should flow through the relief-valve spool. Therefore, the valve tank line should be at ambient temperature.

Many pressure-compensating pumps incorporate a relief valve as a safety backup in case the compensator spool sticks in the closed position (Fig. 4). According to Smiley, the relief valve should be set 250 psi above the pressure-compensator setting. If the relief valve setting is above that of the compensator, no oil should flow through the relief-valve spool. Therefore, the tank lines of these valves should be at ambient temperature.

If, however, the compensator were to stick in the position shown in Fig. 2, the pump will deliver maximum volume at all times and oil not used by the system will return to the tank through the relief valve. “If this occurs, Smiley said, “significant heat will be generated.”

Smiley lamented that plant personnel often randomly adjust the pressures in these systems in an attempt to make the equipment run better. “If the local knob turner turns the compensator pressure above the setting of the relief valve,” he explained, “the excess oil will return to the tank through the relief valve, causing the oil temperature to rise 30 or 40 degrees. If the compensator fails to shift or is set above the relief-valve setting, a tremendous amount [of heat] will be generated.”

Assuming the maximum pump volume is 30 gpm and the relief valve is set to 1,450 psi, the amount of heat generation can be determined using the following formula.

If a 30-hp electric motor is used to drive this system, 25 hp will be converted to heat when in the idle mode. Since 746 W = 1 hp, then 18,650 W (746 x 25) or 18.65 kW of electrical energy will be wasted.

Smiley cited several other heat-generators in hydraulic systems and the importance of maintaining these components. These include accumulator dump valves and air-bleed valves that fail to open, thus allowing oil to bypass to the reservoir at high pressure. He also pointed to heat generated by oil bypassing cylinder piston seals.

If an air-type heat exchanger is used, clean the cooler fins—using a degreaser, if necessary—on a regularly scheduled basis. The temperature switch that controls the cooler fan should be set at 115 F.

If a water-cooled system is used, a modulating valve should be installed in the water line to regulate the flow through the cooler tubes to 25% of the oil flow.

Smiley noted that reservoirs should be cleaned at least annually, lest sludge and other contaminants coat their bottoms and sides. This would allow the reservoir to act as an incubator instead of dissipating heat to the atmosphere.

Smiley offered a final helpful hint for hot-hydraulics troubleshooters: “The next time a heat issue surfaces in one of your hydraulic systems, look for oil flowing from a higher to a lower pressure in the system. That is where you’ll find your problem.” MT

If one of your hydraulic pumps keeps overheating or wearing down, you should repair it soon. Your pump may potentially fail in the future if you don"t repair it fast. Learn why hydraulic pumps overheat or wear down quickly and how to repair your pump below.

Hydraulic pumps work exceptionally hard to keep your machines, cranes, and other equipment functional each day. But over time, pumps can experience issues that interfere with how well they perform each task. One of the main issues with hydraulic pumps is overheating.

Pumps can overheat if too much air enters the system during the day. Air can enter the pump"s housing or cavity through holes and other defects in the machine. Once air enters the system, it can contaminate the fluid inside your hydraulic pump.

A number of other things can trigger problems with your pump, including water, dirt, and debris. If you don"t remove the contaminants properly, they can damage your hydraulic pump before its time.

A contractor can examine your hydraulic pump to see why it overheats constantly. If air is the reason behind your pump"s problems, a contractor can inspect your machine for defects. A contractor may also check the hydraulic system itself for defects.

If a contractor does find defects in your machine or hydraulic system, they"ll seal or repair them for you. A contractor may need to take apart your machine or hydraulic system to make the necessary repairs.

If air isn"t the cause of your pump"s problems, a contractor will measure the temperature inside your machine"s hydraulic system. Hydraulic systems can run hot if they become too old to function well, or if the fluid inside the system is too thin to lubricate the pump and other parts. Using a thicker fluid for your hydraulic system should prevent it from overheating in the future.

A contractor will also check the fluid levels inside your system during the repairs. Low fluid levels can trigger a host of issues with hydraulic systems, including overheating and premature wear and tear. If you don"t maintain the correct fluid levels in your hydraulic system, it can cause the pump to overheat and fail.

When hydraulic oil is getting overheated, there could be several common causes that also cause the system to overheat. First, it is crucial to understand the type of hydraulic system you are using to begin troubleshooting why the system is overheating.

The first cause of hydraulic oil overheating is when the hydraulic equipment system parts and components are nearing the end of their useful lifespans. As they degrade, due to increased internal leakage, they have to work harder to maintain the desired system pressure.

For example, your hydraulic pump is wearing out and needs to be replaced. Due to internal wear pressurised fluid escapes from the high pressure side to the low pressure side generating heat increasing the temperature of the hydraulic fluid and causing circuit overheating.

It is understood that you may want to make system upgrades or changes to customize the system to reflect your specific needs. However, when you do not consider the entire system, it can cause the system to work hard, give off more heat, and increase hydraulic oil temperatures, leading to circuit overheating.

For instance, you may want to increase the fluid flow rate through the system. However, you did not account for the size of hoses and tubing to accommodate the higher flow rates. As a result, the system has to work hard to force the increased flow rates through incompatible hoses and tubes, resulting in more heat generation and fluid overheating.

Tweaking your hydraulic system is perfectly acceptable to optimize its performance. However, where many people go wrong is they only adjust one part of the system and fail to think about how the adjustment will impact other parts of the system.

For example, suppose you make an adjustment to the pump compensator and increase the pressure yet fail to also make a similar adjustment to the relief valve. In this instance the relief valve will blow off more frequently generating more heat and therefore increasing the circuit fluid temperature.

Every component in a hydraulic system imposes a load on the pump, this is referred to as the pressure drop across the particular component. The figure will vary depending upon the flow rate and the energy lost from the fluid due to the pressure drop is converted into heat. If the overall pressure drop across all the components in the circuit unexpectedly increases so the heat generated across the circuit will also increase.

If the fluid is not cooled to compensate for this the fluid temperature continues to increase as the other parts and components generate excessive heat.

If there is dirt, sludge, debris, or water in the hydraulic fluid, the system will generate more heat as it attempts to compensate for the contaminants and push the fluid through the system. Therefore, it is always vital to check your fluid for contamination and change it and or improve fluid filtration when required.

After troubleshooting overheating problems, if you have determined it is not due to the four common causes mentioned above, then there are two general ways you can resolve fluid overheating problems. You can either increase the reservoir capacity to dissipate heat or decrease the amount of heat being generated by the system.

Another way to increase the heat dissipation is to inspect the current heat exchangers, if they are being used, and make the appropriate adjustments. In some cases, you may want to install additional heat exchangers to help reduce the fluid temperature.

To find hydraulic parts, components, and accessories to help you resolve hydraulic oil overheating problems, or if you require assistance in troubleshooting system overheating, please feel free to contact White House Products, Ltd. at +44 (0) 1475 742500 today!

Motors will get hotter is they are converting more power as a percentage of the power input will be lost as heat. More power in, more heat out. You should not run most components with normal hydraulic fluid over 70-80 degrees C as it will lose its lubricating properties and will the damage it causes is exponential.

In addition to the motor are: 2 pumps and a purge valve in the working circuit, a cooler supplied by the purge valve and the pump case drains and a reservoir and header tank. The case drain from the motor returns direct to the reservoir tank.

The working oil temperature has not exceeded 40 degC. The motor overheats before the working oil temperature reaches a temperature at which the cooler will have an effect. Oil temperatures in the case drain line are in the region of 80 - 90 degC once the motor casing reaches 100 degC. Case drain temperatures also show no signs of plateauing. RE: Hydraulic Motor Overheating

The system does not feature motor casing flushing (only a case drain), this is suggested by the motor OEM when motor speeds of 1800RPM are exceeded.What is the motor manufacturer? Is there datasheet available? RE: Hydraulic Motor Overheating

Thanks for the reply. The motor manufacturer is Parker and it is a F12-250 frame size motor. See below link for product literature, see page 67 for information detailing a recomendation for case flushing above 1800 RPM.

The datasheet invites you to ask Parker for more specific efficiency information for your particular frame size - please do this and then post the graphs for this forum. Somebody here will be able to show you how to interpret the graphs and estimate whether or not you need to flush the motor case. Also let us know what oil you are using because this may have a bearing on the matter.

Actually, you already know that you do need to flush the motor case because of the temperatures you are experiencing. The datasheet suggests you don"t need flushing but 1600 rpm is very like 1800 rpm and your working pressure is quite high. It"s not so black and white as 1799 rpm means flushing is NOT required and 1801 rpm means flushing IS required. It may be the case that the particular build up of manufacturing tolerances has meant you received a motor which is a bit tight (internal friction is a little high - resulting in more power loss but also resulting in a smallish case drain flow - so there isn"t enough case flow to take away the waste power - and that is why you are getting such a high case temperature).

Oil temperatures above 60 deg C can result in scalding/scarring if any escaping fluid contacts the skin (below this temperature getting soaked with the oil is just irritating, above this temperature it constitutes an injury).

The oxidation rate of the oil is very temperature dependant, doubling for every 10 deg C increase in temperature. Having very hot oil shortens its service life.

The very hot oil in the case will have a low viscosity and this will rapidly decrease the service life of the motor bearings. In a bent axis motor the shaft bearings work very hard.

I think you"ve taken the brochure wording a little bit too literally. The wording states that continuous operation "may require case flushing" and the limits are those which flushing is "usually required". Given you"re at 1600 rpm versus 1800rpm for the "usual" limit, then it would appear that the vendor has covered himself.

The amount of heat generated will be approximately the power input times (1-efficiency). There are equations in the first part of the book to work this put which needs flow as well as pressure. Given that there are no cooling vanes, whilst a lot of the heat will escape via the hydraulic fluid, enough will reomain to heat up the casing quite quickly as you"ve discovered.

I have received efficiency graphs from Parker for the 250 size motor, I have however been unable to upload them on to this thread. Reading the graphs I have estimated a volumetric flow efficiency of 97%, a mechanical efficiency of 97% and total efficiency of 94%. This does however seem a little high? From this and the pumps theoretical power output (174kW) I have estimated that 11kW of heat will be generated. What I am now trying to calculate is how much heat will be removed through discharge of fluid from the motor and how much will be left in the motor casing through convective heat transfer. Or perhaps I am going about this in the wrong way?

I fully appreciate that the Parker manual uses terms such as "may" and "usually" and that it is very much application specific. And It is clear that a flushing system is required. I would however like to apply some theory behind the application to ensure that my seniors are confident that this application is being investigated and justified thoroughly. What steps would you advise to follow once efficiency has been calculated to calculate heat dissipated by the fluid and heat remaining in the casing?

Looks like you"re nearly there. Measure temp in versus temp out of the hydraulic fluid x flow x thermal capacity and you have a good guess as to heat being carried away by the fluid. What"s left is basicaly heating the case up, so even if it"s 1kW, that 1kW into a relatively small thing with not much heat loss capacity other than convection - which won"t be much. You could get really scientific and apply some sort of water cooling blanket to calcualte the heat being generated in the casing and then show that without additional cooling the motor would simply continue to heat up.

If you had a 175 kW electrical motor and no fan on it then it would also get red hot. Electrical motor efficicieny at that size is about the same. Would you think that you could install an electrical motor that big and not cool it? Ok it doesn"t have fluid taking some of the heat away, but even so...

Here’s the quick and dirty calculation of drain oil temperature (there’s too many unknowns in the actual performance of your particular motor and too little precision in your efficiency data to warrant doing a more sophisticated calculation).

Your motor is 250 cc/rev and running at 1600 rpm so your theoretical input flow would be 400 L/min. But your volumetric efficiency is 97% so your actual input flow will be 400/0.97 = 412 L/min and we can assume that the extra 12 L/min you needed becomes your case drain flow. (You could quite easily measure your case drain flow using a measuring flask and a stopwatch.)

This case drain oil came from your 300 bar supply so will be warm because it will have reduced its pressure to 0 bar by passing through the clearances in the motor. Assume a temperature rise of 6.8 deg C per 100 bar which means your case drain oil “source” is now 20.4 deg hotter than the supply.

The theoretical shaft output power from your remaining 400 L/min at 300 bar should be 200 kW but your mechanical efficiency is 97% so you lose 3% of 200 kW, i.e., 6 kW. This heat has to be carried away by your 12 L/min case drain flow.

The specific heat capacity of a typical mineral oil is 1.67 J/g/K and the typical density is 0.88 g/cc. Your flow of 12 L/min is 200 cc/sec so that’s 176 g/sec. Your heat input is 6 kW, i.e., 6000 J/sec so the energy input to the oil is 34 J/g. The temperature rise because of this energy input will be 34/1.67 = 20.4 deg C (yes, it’s the same as the temperature rise from the pressure drop but that’s because both of your efficiencies are numerically equal).

As I stated earlier, this is a horribly simplistic calculation because no account is taken of: the compressibility of the oil, heat taken away from the motor by the outlet [return] flow, conduction through whatever the motor is bolted to, convection from the motor case etc. All I wanted to do was show you how the numbers stack up.

If you were to apply some motor case flushing flow this would be taken from the low pressure side of the circuit (say 20 bar) which would be from the output side of the motor. So let’s assume a bulk oil temperature of 60 deg C and the temperature of the motor supply oil would be about the same. Call the motor outlet temp 62 deg C so that will give you a flushing flow inlet temp of about 64 deg C. A flushing flow of, say, 20 L/min at this 64 deg C would add to your case drain “source” flow of 12 L/min at 80.4 deg C to give you 32 L/min at ~70 deg C. This combined flow now has to absorb the 6 kW wasted mechanical power; the resulting temperature rise will be ~7.6 deg C and your case drain oil would be coming out of the motor at just under 80 deg C.

If you added a separate hot oil shuttle valve to your motor circuit with an adjustable throttle valve on the shuttle outlet you could vary the amount of flushing flow until you brought the case drain exit oil temperature back into line. Do check, however, that your boost pump has enough capacity to do this – if you take too much flow off the motor outlet circuit then the boost pressure may drop too low for the pump’s comfort. Alternately, you could redirect some of the flow from your existing purge valve if it is close enough to the motor. Remember that increasing the case flushing flow will decrease the flow through your cooler so its cooling performance will be reduced. Is it possible that you could redirect the motor case drain flow through the cooler as well (as long as the motor case and pump case can take the cooler back pressure)? If you could do this the cooler performance would increase because of the greater flow and the greater average temperature difference.

Since actual heat transfer (24.48 kW) is significantly greater than the calculated heat generated through volumetric inefficiencies (6.96 kW), this would suggest that there is a problem within the hydraulic motor and the motor should be replaced.

Your colleague seems to be taking everything as conservative. You say the Vol eff is 97%, so flow is less. Also density will be lower at higher temp, say 0.8. This gives 0.16kg/sec. Can"t you measure actual case drain flow then weigh it??

Reference the following point: "This case drain oil came from your 300 bar supply so will be warm because it will have reduced its pressure to 0 bar by passing through the clearances in the motor. Assume a temperature rise of 6.8 deg C per 100 bar which means your case drain oil “source” is now 20.4 deg hotter than the supply."

Can you confirm how you estimated the 6.8 deg C per 100 bar. I have been trying to understand the relationship between reducing pressure and a temperature increase. Or how can I estimate the heat generated through a pressure reduction, do i need to know delta T to calculate this?

Suppose you had a flow of 60 L/min at 100 bar, the [theoretical] power you would need to pump this would be: 60 x 100 / 600 = 10 kW. If you then let this source of pressurised oil de-pressurise by passing over a jet (or some other clearance passage within a hydraulic component) then no “real” work will have been done and the original power input of 10 kW will all be converted to heat.

60 L/min = 1 Litre/sec = 0.88 kg/sec (assuming that the fluid density is 880 kg/m³). Your input power of 10 kW is 10 kJ/sec so you will be putting 10 kJ/sec into 0.88 kg/sec, i.e., 10 kJ into 0.88 kg. This equates to 11.36 kJ/kg.

The specific heat capacity of the oil is typically 1.67 kJ/kg/K so the temperature rise will be 11.36/1.67 = 6.8 K for a 100 bar pressure drop. If the pressure drop were higher the energy input would be higher and the temperature rise would be higher. Similary a lower pressure drop creates a lower temperature rise. To be more specific the temperature rise is 0.068 K/bar.

I’ve used real numbers in this example, but you should be able to see that the flow rate is actually of no consequence. If the flow had been 120 L/min then the input power would have been 20 kW … but this would have been dissipated into 1.76 kg/sec so the specific energy input would still have been 11.36 kJ/kg.

If your motor is new then you can think of it behaving just like a rebuilt engine that hasn"t fully run in yet. It will be "tight" so there will be a poor mechanical efficiency and a good volumetric efficiency. The overall efficiency may still be good [this is a measure of the motor"s abilty to convert the hydraulic input power (pressure x flow) into mechanical output power (torque x shaft speed)]. The [poorish] mechanical efficiency means that some of the mechanical power is lost inside the motor - but the [high] volumetric efficiency means that there isn"t much leakage flow available to take the wasted power away - hence your high case drain temperature.

Hyundai hydraulic pumps are integral parts of excavators. The company is the third largest manufacturer in the world. As one of the leading brands, Hyundai has been popularized after producing high quality and durable products over time.

An excavator Hyundai hydraulic pump can overheat for a variety of reasons. The most common cause is actually running the pump at too low of an RPM. When the pump is not turning fast enough, it can’t move the oil through the system quickly enough and it starts to overheat. Another common cause is a blockage in the system somewhere. This could be a blockage in the suction line, return line, or even in the pump itself. If there is a blockage, the oil can’t flow properly and it will start to overheat.

If your excavator Hyundai hydraulic pump is overheating, there are a few things you can do to try and fix the problem. First, check the RPM of the pump. If it is running too low, increase it until it is running at the proper speed. Next, check for any blockages in the system. If you find one, clean it out and see if that fixes the problem. Finally, if neither of those two things works, you may need to replace the pump itself.

There are many potential causes of an excavator Hyundai hydraulic pump overheating. The most common cause is a loss of hydraulic fluid due to a leak in the system. Other causes can include a build-up of dirt and debris in the system, or a problem with the pump itself.

If you suspect that your excavator’s hydraulic pump is overheating, the first step is to check for leaks. If you find a leak, make sure to repair it as soon as possible. If there is no leak, then you will need to clean out the system to remove any dirt or debris that may be causing the problem.

If you are still having problems with your excavator’s hydraulic pump overheating, it may be necessary to replace the pump itself. This is a more complex repair, so it is best to consult with a qualified mechanic or dealer before proceeding.

There are several potential causes of an excavator Hyundai hydraulic pump overheating, but the most common cause is simply because the pump isn’t getting enough oil. This can happen for a variety of reasons, such as a leaking oil line or an incorrect amount of oil being used. Another potential cause is that the pump isn’t getting enough cooling water, which can be caused by a clogged water filter or an insufficient water supply. Whatever the cause, it’s important to get the problem fixed as soon as possible to avoid damage to the pump.

The Hyundai hydraulic pump is located in the engine bay of the excavator. It is responsible for providing hydraulic pressure to the excavator’s hydraulic system. If the pump overheats, it can cause damage to the hydraulic system and potentially lead to a loss of excavator performance. There are a few things that you can do to prevent the pump from overheating:

– Inspect the pump regularly for any potential leaks. Leaks can cause the fluid level to drop and also allow air to enter the system, which can cause problems.

If you’re noticing that the Hyundai hydraulic pump on your excavator is overheating, there are a few things you can do to prevent it. First, make sure that the pump is getting enough oil. If the pump isn’t properly lubricated, it will overheat. You should also check the cooling system to make sure it’s working properly. If the pump is still overheating, you may need to replace the seals or bearings.

If you have an excavator Hyundai, you may have experienced your hydraulic pump overheating. This can be a major problem, as it can lead to damaged equipment and even injuries. However, there are a few things you can do to help prevent this from happening. make sure that your excavator is properly ventilated. Second, check the fluid levels in your hydraulic system regularly. Third, use aHydraulic Pump Overheating Prevention Kit. By following these simple tips, you can help ensure that your hydraulic pump doesn’t overheat and cause damage to your equipment or yourself.

A system malfunction is taking shape, and a hydraulic fluid overheating problem is causing major headaches. If the equipment owner is to avoid popping a painkiller, he needs to know what’s behind the heat generating riddle. On identifying the thermal energy source, only then can a remedy be implemented. Let’s start with a quick fluid temperature check, just like the ones patients undergo when a nurse approaches with a thermometer.

On measuring the temperature of the system fluid, the gauge needle is wobbling around the 80°C mark. That’s a worry, and the operator isn’t going to run the equipment while it’s this hot. The elastomeric seals and hoses start to deteriorate when the oil is roasting hot like this, and the rigid equipment alloys seem warm enough to fry an egg. If the temperature rises higher, the fluid is going to degrade while the seals experience permanent damage. Turn the gear off until a solution can be traced.

Referring back to a human patient, low blood pressure problems cause the heart to work harder. Likewise, low fluid pressures occur because of obstruction. Like a clogged artery, a blocked hose or sharply bent fluid channel stops the oil from flowing. Undersized components are also responsible for this pressure attenuating effect. With the fluid hampered, the system responds by generating thermal energy. Next, has the equipment been altered? Someone maybe felt the gear needed a little more “oomph,” so they jury-rigged the pump compensator. Finally, when aging components don’t work productively any longer, they produce heat, which is then transmitted into the oil.

It’s not always easy to find that single aging part, not from the outside. Happily, a temperature measuring instrument can find the culprit part by measuring thermal gains across discrete components. As for clogs and undersized parts, they’re correctable, too. Replace the components and remove all sharp hose turns. And, here’s a problem that shouldn’t occur, don’t let amateur hour workers ruin expensive pieces of hydraulic equipment. Don’t let someone introduce a radical system improvement. Pump compensator should only ever be adjusted by a trained repair engineer.

The main culprits have been identified and addressed, but there are always other problems to deal with when mobile hydraulic equipment runs hot. It’s a serious problem. The equipment is aging, the seals are failing, and the oil is separating. Worse still, a serious burn is likely because someone could fall against a hot metal part. If the issue continues, call out a qualified repair technician, for this situation cannot be allowed to persist.

It’s that time of year again and all over the country there are hydraulic systems overheating.  Some of them overheat every summer, but most of them usually just run a little warmer with increases in ambient temperature.  What is causing it?  Often a dirty or poorly placed heat exchanger can be the culprit.  Sometimes a bypassing check valve across the heat exchanger can make the system overheat.  Unless the design of the system has been changed in some way, it is very unlikely that adding a heat exchanger is the answer.  Systems that overheat are simply not operating efficiently and there is usually an easily corrected cause.  Here are four of the more common causes of overheating that we find.

By far the most common cause of overheating that we find is an improper adjustment.  On machines that usually do not overheat but are overheating now, this is the first thing we look for.  The most common component that gets out of adjustment is the pump compensator.  It is imperative that the compensator be set below the system relief valve.  But for whatever reason, someone decides that the system would run better at a higher pressure.  The compensator setting then gets increased, but the relief valve setting does not.  Once the compensator setting approaches the relief valve setting, the relief valve starts to crack open and dump oil flow to tank.  The more the compensator setting is increased, the more the relief valve opens and the more flow returns to tank.  Instead of varying its flow to meet the demands of the system as it is designed to do, the pressure compensating pump moves to full stroke behaving as a fixed displacement pump.  Any flow not used to move a load returns to tank through the relief valve.  At system idle, ALL of the pump flow returns to tank.  Since the resulting pressure drop doesn’t do any work, virtually all of the energy going into the system is converted to heat causing the fluid temperature to soar.

Changing the system pressure is usually a bad idea.  Most systems have designer recommendations for system pressure and a lot of design criteria are taken into consideration to determine the optimum system pressure.  Often the pressure is increased in an attempt to speed up the machine but this is a very inefficient way to accomplish this.  Flow rate, not system pressure, determines the speed of the actuator.  Yes, turning up the pressure will often also increase the flow, but the more efficient way is to open a flow control or raise the setting of the manual volume adjustment.  In the absence of designer recommendations, we usually recommend that the system relief valve be set approximately 250 PSI above the pump compensator.

In Figure 1 above, the system is adjusted correctly.  The pressure compensating pump is capable of delivering as much as 30 GPM.  With only the directional valve on the left open, the system uses 10 GPM so the pump will stroke only enough to maintain 1200 PSI in the system delivering 10 GPM.  When the second directional valve opens in Figure 2, the pump stroke increases to 20 GPM to maintain the 1200 PSI setting.  But in Figure 3, the compensator setting has been increased to 1600 PSI.  The relief valve however is set below that amount at 1450 PSI.  In an attempt to reach 1600 PSI in the system, the pump will stroke to its maximum 30 GPM.  The system only uses 10 GPM leaving 20 GPM to dump across the relief valve generating heat.  We can calculate the heat that is generated using the formula HP = PSI X GPM X .000583 and we see that an extra 17 HP is generated.  In Figure 4, the system is at idle.  The pump will remain at full stroke however dumping its full 30 GPM across the relief valve.  This generates a whopping 25 HP in excess heat!

This is one that we find most often in systems that have been modified from their original design.  One of the more common system upgrades is a higher flow pump to increase speed, but the system piping and hoses may not get the same upgrade.  The result is that it takes more pressure just to push the oil to the actuators to do the work.  For example, 20 GPM will flow through a #10 SAE hydraulic hose at a fluid velocity of 20 feet per second, but if the hose is replaced by a #12 SAE, the fluid velocity drops to only 15 feet per second.  This simple size increase reduces the restriction by 25%.  Tight radius bends in pipe will also increase turbulence in the lines.  Whenever the system flow rate is increased by installing a higher flow pump, check pipe and hose charts to ensure the system can withstand the greater flow rate without an excessive increase in fluid velocity.  In the absence of designer recommendations, we usually recommend that fluid velocity be kept between 2 – 5 fps in pump suction lines, 10 – 15 fps in return lines and 15 – 20 fps in pressure lines (for systems up to about 3000 PSI)  Above 3000 PSI, the system designer will usually specify how many bends can be in the system piping and what radius they must be.  This avoids the necessity of exceptionally large piping in higher pressure systems.

As components wear, internal bypassing increases.  Oil that bypasses across the tight tolerances of a component undergoes an immediate pressure drop that performs no work.  Heat is the inevitable result.  The more bypassing that occurs, the more heat is generated.  Some components are notorious heat generators even when brand new.  Servo valves,  proportional valves and flow controls all generate heat from the time they are new because they always have a pressure drop across them.  So how do we know if a component needs to be replaced in order to keep the temperature down?  The best way is to routinely measure the temperature gain at various components in the system.  Keep a record of these measurements and use them to help locate troublesome worn components.

One of the primary purposes of the reservoir is to radiate heat to atmosphere.  You may have wondered why your hydraulic reservoir is rectangular in shape while most other tanks you see are round.  The most efficient use of volume, i.e. the maximum volume with minimum surface area, is a sphere.  This may be desirable in some applications, but in a hydraulic system we want more surface area to radiate heat, not less.  When a system is designed, the reservoir is sized based on a number of factors such as how much the oil level will rise and lower with the operation of cylinders, how long oil should remain in the reservoir to allow contaminants to sink to the bottom and how much heat will need to radiate to atmosphere.  If a higher flow pump is installed, the oil will not stay in the reservoir long enough to dissipate heat.  Also, when a variable displacement pump is used, oil from the pump case drain is ported directly to tank.  A higher flow pump will also have a higher case drain flow.  Most variable displacement pumps will bypass approximately 1 – 3% of its maximum flow rate.  Case flow is very hot because it is oil that has just bypassed across the tight internal tolerances inside the pump.  A higher case flow will raise operating temperature if a larger reservoir is also not part of the upgrade.

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