tractor hydraulic pump pressure in stock

A hydraulic system works under three key principles: A liquid can’t be compressed; resistance to flow is the only way to create pressure in a system; and energy created under pressure will yield either work or heat.

The heart of a hydraulic system is a positive-displacement pump that is either of a fixed-displacement or a variable-displacement style. Either of these pump styles can be a gear, a vane, or a piston design.

On the other hand, a variable-displacement pump can alter the volume of oil it moves with each cycle even if the operating speed stays the same. This design is employed in applications where a specific pressure or flow must be maintained.

Most early hydraulic systems used on tractors were open-center designs. As farmers grew more dependent on hydraulics, their systems advanced to a closed-center system and finally to a load-sensing system.

With an open-center system, the pump produces a continuous flow of oil that must return to the reservoir when the cylinder or other actuator is not being moved. When flow is directed via a control valve to a cylinder, the oil volume stays constant. However, the oil pressure is increased to the level necessary to perform the work.

When the control valve is released, the fluid remains trapped in the cylinder, and the workload is supported. The pump pressure goes down and flow increases.

Pump displacement and, thus, flow, changes to meet the demand required. When no function is required, oil flow is blocked at the control valve. When one (or more) control valve is opened, the pump automatically adjusts the delivery rate (volume) to satisfy the demand. Pressure to the valves will be maintained as long as the pump volume is sufficient to meet the demand.

Today, it is common to find a load-sensing system in use on tractors, particularly high-horsepower models. It is a modification on the closed-system design. This design permits stand-by pressure to be low when the control valve is in neutral.

When you move the control valve, flow is designed to maintain a pressure slightly higher than the highest pressure needed in the system. It regulates flow based on the pressure required to move the load rather than based on the pump output.

One reason for this is that this oil does more than perform work. It must lubricate moving parts, be chemically stable at high temperatures and pressures, protect parts from rust and corrosion, resist foaming and oxidation, and be capable of separating itself from air, water, and other contaminants.

Hydraulic oil must also maintain a designated viscosity while operating in a wide temperature range. Viscosity is a fluid’s resistance to flow. It is the thickness at a defined temperature set by the Society of Automotive Engineers.

All petroleum-base oils tend to thicken when they are cold, and they become thinner when heated. If the viscosity is too low (or thin), it can cause leakage past the seals. But if the fluid is too thick (high viscosity), sluggish operation of the hydraulics occurs along with an additional power drain on the engine.

Farm equipment hydraulic systems are fitted with components that have very tight and exacting tolerances. As a result, they require hydraulic oil that has a high viscosity index and also has lubricating qualities paramount to long life. Good oil will be able to cling to close-fitting parts even under high temperatures. Many tractors use the hydraulic oil to lubricate the transmission. Low-quality hydraulic oil will provoke excess wear in the hydraulics and transmission.

Ensuring a smooth operating hydraulic system is quite basic. You need to remember that hydraulic oil does wear out over time and needs to be changed. Often the additives in the oil (which are essential to its performance) become consumed. Plus, oil also absorbs dirt and moisture over time, compromising its ability to perform, let alone prevent corrosion of key components, seals, and gaskets. One sign of worn-out oil is components that stick when operating. This is especially true of control valves.

When purchasing hydraulic fluid, make sure the brand meets or exceeds the requirements for your machine as dictated in the owner’s manual. Equipment manufacturers have application-specific requirements for the oil. Even though you may save a few dollars selecting a cheaper oil, it may cost you in the long run. That same advice is true when selecting hydraulic filters.

When buying fluid, only purchase what you need for that season, because hydraulic oil can get old (their additives can precipitate out of the oil with time). Be sure to always store fluids in a shop that has minimal temperature variation to avoid condensation from forming in the storage container and polluting new oil.

From time to time, listen to the hydraulic system operation and watch how well it performs. These efforts can tell you that something is going wrong long before a major problem occurs.

Proper service intervals are meaningless if a hydraulic system isn’t kept clean. Always use the dust caps on coupler valves and wipe off any fitting or service port before opening up or closing.

Keep the hydraulic system’s exterior clean by simply washing with a pressure wash, as dirt left around seals and dipsticks eventually work into the fluid.

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Check that the pump shaft is rotating. Even though coupling guards and C-face mounts can make this difficult to confirm, it is important to establish if your pump shaft is rotating. If it isn’t, this could be an indication of a more severe issue, and this should be investigated immediately.

Check the oil level. This one tends to be the more obvious check, as it is often one of the only factors inspected before the pump is changed. The oil level should be three inches above the pump suction. Otherwise, a vortex can form in the reservoir, allowing air into the pump.

What does the pump sound like when it is operating normally? Vane pumps generally are quieter than piston and gear pumps. If the pump has a high-pitched whining sound, it most likely is cavitating. If it has a knocking sound, like marbles rattling around, then aeration is the likely cause.

Cavitation is the formation and collapse of air cavities in the liquid. When the pump cannot get the total volume of oil it needs, cavitation occurs. Hydraulic oil contains approximately nine percent dissolved air. When the pump does not receive adequate oil volume at its suction port, high vacuum pressure occurs.

This dissolved air is pulled out of the oil on the suction side and then collapses or implodes on the pressure side. The implosions produce a very steady, high-pitched sound. As the air bubbles collapse, the inside of the pump is damaged.

While cavitation is a devastating development, with proper preventative maintenance practices and a quality monitoring system, early detection and deterrence remain attainable goals. UE System’s UltraTrak 850S CD pump cavitation sensor is a Smart Analog Sensor designed and optimized to detect cavitation on pumps earlier by measuring the ultrasound produced as cavitation starts to develop early-onset bubbles in the pump. By continuously monitoring the impact caused by cavitation, the system provides a simple, single value to trend and alert when cavitation is occurring.

The oil viscosity is too high. Low oil temperature increases the oil viscosity, making it harder for the oil to reach the pump. Most hydraulic systems should not be started with the oil any colder than 40°F and should not be put under load until the oil is at least 70°F.

Many reservoirs do not have heaters, particularly in the South. Even when heaters are available, they are often disconnected. While the damage may not be immediate, if a pump is continually started up when the oil is too cold, the pump will fail prematurely.

The suction filter or strainer is contaminated. A strainer is typically 74 or 149 microns in size and is used to keep “large” particles out of the pump. The strainer may be located inside or outside the reservoir. Strainers located inside the reservoir are out of sight and out of mind. Many times, maintenance personnel are not even aware that there is a strainer in the reservoir.

The suction strainer should be removed from the line or reservoir and cleaned a minimum of once a year. Years ago, a plant sought out help to troubleshoot a system that had already had five pumps changed within a single week. Upon closer inspection, it was discovered that the breather cap was missing, allowing dirty air to flow directly into the reservoir.

A check of the hydraulic schematic showed a strainer in the suction line inside the tank. When the strainer was removed, a shop rag was found wrapped around the screen mesh. Apparently, someone had used the rag to plug the breather cap opening, and it had then fallen into the tank. Contamination can come from a variety of different sources, so it pays to be vigilant and responsible with our practices and reliability measures.

The electric motor is driving the hydraulic pump at a speed that is higher than the pump’s rating. All pumps have a recommended maximum drive speed. If the speed is too high, a higher volume of oil will be needed at the suction port.

Due to the size of the suction port, adequate oil cannot fill the suction cavity in the pump, resulting in cavitation. Although this rarely happens, some pumps are rated at a maximum drive speed of 1,200 revolutions per minute (RPM), while others have a maximum speed of 3,600 RPM. The drive speed should be checked any time a pump is replaced with a different brand or model.

Every one of these devastating causes of cavitation threatens to cause major, irreversible damage to your equipment. Therefore, it’s not only critical to have proper, proactive practices in place, but also a monitoring system that can continuously protect your valuable assets, such as UE System’s UltraTrak 850S CD pump cavitation senor. These sensors regularly monitor the health of your pumps and alert you immediately if cavitation symptoms are present, allowing you to take corrective action before it’s too late.

Aeration is sometimes known as pseudo cavitation because air is entering the pump suction cavity. However, the causes of aeration are entirely different than that of cavitation. While cavitation pulls air out of the oil, aeration is the result of outside air entering the pump’s suction line.

Several factors can cause aeration, including an air leak in the suction line. This could be in the form of a loose connection, a cracked line, or an improper fitting seal. One method of finding the leak is to squirt oil around the suction line fittings. The fluid will be momentarily drawn into the suction line, and the knocking sound inside the pump will stop for a short period of time once the airflow path is found.

A bad shaft seal can also cause aeration if the system is supplied by one or more fixed displacement pumps. Oil that bypasses inside a fixed displacement pump is ported back to the suction port. If the shaft seal is worn or damaged, air can flow through the seal and into the pump’s suction cavity.

As mentioned previously, if the oil level is too low, oil can enter the suction line and flow into the pump. Therefore, always check the oil level with all cylinders in the retracted position.

If a new pump is installed and pressure will not build, the shaft may be rotating in the wrong direction. Some gear pumps can be rotated in either direction, but most have an arrow on the housing indicating the direction of rotation, as depicted in Figure 2.

Pump rotation should always be viewed from the shaft end. If the pump is rotated in the wrong direction, adequate fluid will not fill the suction port due to the pump’s internal design.

A fixed displacement pump delivers a constant volume of oil for a given shaft speed. A relief valve must be included downstream of the pump to limit the maximum pressure in the system.

After the visual and sound checks are made, the next step is to determine whether you have a volume or pressure problem. If the pressure will not build to the desired level, isolate the pump and relief valve from the system. This can be done by closing a valve, plugging the line downstream, or blocking the relief valve. If the pressure builds when this is done, there is a component downstream of the isolation point that is bypassing. If the pressure does not build up, the pump or relief valve is bad.

If the system is operating at a slower speed, a volume problem exists. Pumps wear over time, which results in less oil being delivered. While a flow meter can be installed in the pump’s outlet line, this is not always practical, as the proper fittings and adapters may not be available. To determine if the pump is badly worn and bypassing, first check the current to the electric motor. If possible, this test should be made when the pump is new to establish a reference. Electric motor horsepower is relative to the hydraulic horsepower required by the system.

For example, if a 50-GPM pump is used and the maximum pressure is 1,500 psi, a 50-hp motor will be required. If the pump is delivering less oil than when it was new, the current to drive the pump will drop. A 230-volt, 50-hp motor has an average full load rating of 130 amps. If the amperage is considerably lower, the pump is most likely bypassing and should be changed.

Figure 4.To isolate a fixed displacement pump and relief valve from the system, close a valve or plug the line downstream (left). If pressure builds, a component downstream of the isolation point is bypassing (right).

The most common type of variable displacement pump is the pressure-compensating design. The compensator setting limits the maximum pressure at the pump’s outlet port. The pump should be isolated as described for the fixed displacement pump.

If pressure does not build up, the relief valve or pump compensator may be bad. Prior to checking either component, perform the necessary lockout procedures and verify that the pressure at the outlet port is zero psi. The relief valve and compensator can then be taken apart and checked for contamination, wear, and broken springs.

Install a flow meter in the case drain line and check the flow rate. Most variable displacement pumps bypass one to three percent of the maximum pump volume through the case drain line. If the flow rate reaches 10 percent, the pump should be changed. Permanently installing a flow meter in the case drain line is an excellent reliability and troubleshooting tool.

Ensure the compensator is 200 psi above the maximum load pressure. If set too low, the compensator spool will shift and start reducing the pump volume when the system is calling for maximum volume.

Performing these recommended tests should help you make good decisions about the condition of your pumps or the cause of pump failures. If you change a pump, have a reason for changing it. Don’t just do it because you have a spare one in stock.

Conduct a reliability assessment on each of your hydraulic systems so when an issue occurs, you will have current pressure and temperature readings to consult.

Al Smiley is the president of GPM Hydraulic Consulting Inc., located in Monroe, Georgia. Since 1994, GPM has provided hydraulic training, consulting and reliability assessments to companies in t...

Good catch. I forgot the 1300 and 1300F have different ratings on the hydraulics. I wonder why there is a difference between the two (?) I"d be surprised if anything physically is different hydraulically between the 1300 and 1300F version other than the relief valve setting. Can we get some input here from the original designers of these things? :wave: LOL

I also noticed the TX1300 (F) on tractordata.com shows a rear lift weight of 838 lbs. which is what they claim for the 2160 despite it running higher hydraulic pressure. Again my field tests show the 2160 can lift more. Interesting...

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is a fixed clearance, all cast iron construction pump.  Designed to replace Webster/Danfoss HC series. We also use this in transmission charge pump applications.

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