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Commercial Intertech Pumps and Motors
Repair Parts, Hydraulic Pumps, Motors, and Valves

Load sensing or flow on demand system may employ a variable or fixed displacement pump. Load-sense controls on piston pumps regulate the flow to the control valve by positioning the pump swashplate. The control mechanism is usually adjustable from 200-300 psi (14-20 bar). It compares the pressure at the outlet of the pump to the loadsense pressure signal coming from the valve and increases or decreases flow to reach equilibrium. Equilibrium results when the pressure differential between the outlet of the pump and load-sense signal of the valve reaches a pre-determined value referred to as margin pressure.

When a gear pump is used with a bypass unloader, the function of the unloader is similar to the load-sense control mechanism on the piston pump. The unloader senses the output pressure at the pump vs. the load-sense signal from the control valve. The unloader regulates flow to the valve until the flow requirements, as defined by the margin pressure requirements of the bypass unloader, are met. Excess flow is unloaded to tank at a pressure slightly higher than the operating pressure of the valve.

When the metering notches of the control valve spool are open a small amount very little flow is needed to satisfy the margin pressure requirement. Stroking the valve spool farther causes the load sense control to increase pump stroke until margin pressure is attained. Conversely, reducing the control valve stroke will cause the control to destroke the pump to meet the new flow requirement.

The following are advantages of load-sensing pressure-compensated valves that positively impact the performance of your machine:

Metering is independent of load. Changes in pressure due to load variation do not affect the output flow of the valve. This provides predictable speed control and makes the operator’s job easier.

Simultaneous metering is generally unaffected by changes in pressure due to load changes. Therefore, the operator does not waste time throttling flow to two function with changes in load. This improves productivity and reduces operator fatigue.

Lower flow forces translate into lighter lever effort on manually operated valves, thus reducing operator fatigue.

Flow forces within the valve are more linear vs. spool stroke, resulting in lower hysteresis for pilot operated control valves. This improves the predictability of actuator speed vs. operator command.

Horsepower consumption is optimized when Commercial’s PC25 or PC55 is interfaced with a PVO™ piston pump, because only the flow requested by the valve is delivered.

When a PC25 or PC55 is applied with a gear pump and a bypass unloader, the bypass unloader will deliver only the flow requested by the valve. Any excess flow will return to tank at a pressure slightly above the highest loaded function.



Commercial Intertech’s PC25 and PC55 family of load-sense individually pressure-compensated valves offers an advancement in technology and performance that provides a significant improvement in machine design and controllability.

The family of valves consists of two frame sizes and accommodates flow requirements from 10-70 gpm (38-265 lpm). The PC25 is rated at 10-45 gpm (38-170 lpm), and the PC55 is rated at a maximum flow of 75 gpm (285 lpm). Both valves are rated at 4000 psi (275 bar).

The design incorporates Overdemand Management TechnologyTM (OMT) that automatically compensates during pump overdemand to maintain proportional flow to each function, but at a reduced volume. Therefore, the operator is able to maintain the rhythm of the machine and maximize productivity. Additionally, the correction made by the valve makes the operator aware of the overdemand condition enabling smooth execution of the appropriate action.

Inherent in this type of design is the routing of the highest load-sense pressure to the spring end of all the section compensators or flow controls. This enables the valve to adjust to a pump overdemand situation. This design benefit requires that allowances be made for induced loads exceeding the inlet pressure defined by the load-sense relief valve. Otherwise, all of the compensators would close during this condition and no flow would be available. Induced loads are common on excavators, wheel loaders, and backhoes. This phenomenon is addressed by a check in the work section that routes the high pressure signal to the spring end of the compensator and forces it to close. To prevent this signal from closing the other compensators, it is routed to the outlet where it is conditioned and then sent to the spring end of the other compensators.

To maximize the speed of response, there is a dedicated pathway for the load-sense signal to the pump. No poppets have to be moved or springs compressed to get the highest load pressure into this logic circuit. This is especially beneficial on applications where low standby pressures are required.

Other Key Features:

Symmetrical work section housing permits operators at either Port A or B ends of the valve.

Compensator efficiency is well above the nominal flow rating of the valve.

Uses the same port accessories and spool positioning devices as the VA/VG20 series.

Can accept a load-sense signal from an external valve and send the highest signal back to the pump.

Porting (maximum): Inlet - High Pressure: SAE 16, 1” BSP, M33. Low Pressure: SAE 16, 1” BSP, M33. Work-section - SAE 12, 3/4” BSP, M26. Outlet - SAE 20, 1 1/4” BSP, M42. Gauge and Load-sense - SAE 6, 1/4” BSP, M14.

Product Options

Inlet with a clipper relief valve and/or integrated pressure reducing valve.

Work-sections, 3-position; 4-position float and 4-position regeneration.

Spool positioners - spring-return; (3) position detent; spring-return/detent; pneumatic; on/off and proportional solenoids; hydraulic-remote and electric-proportional (Digitrak).

Port accessories - relief valves; lockout relief valves; relief valves/anti-cav’s; anti-cav’s; vented anti-cav’s and port restrictors.

To noticeably improve the controllability of your machine or to take advantage of the increased efficiency of a load-sense system, choose the PC25/ PC55. When properly sized with a PVO piston or Commercial Intertech gear pumps, the PC25/PC55 assures you of an engineered match that will provide predictable performance and reliability.

Specifications:

Nominal Flow Rating - 45 gpm (170 lpm)
Operating Pressure - 4000 psi (275 bar)
Exhaust Pressure - 300 psi (21 bar) Margin Pressure - 250 psi (17 bar) - recommended
Filtration Required - ISO 18/14 Solenoids - ISO 17/14 Fluid - Mineral Based Hydraulic Oil
Fluid Temperature and Viscosity Range -20° to 200°F (-29°C to 150°C)
Number of work sections -10
Weight (approx.) - Inlet 16.1 lbs., Outlet 15.4 lbs.

D.A. & 4 Position Regen., 4 Position Float
Manual 14.2 14.9
Hydraulic Remote 16.5 19
Solenoid 22
Digitrak 22



Description of Operation



When the spool is in neutral, the pump is connected to the inlet core which is deadblocked at the outlet of the valve. The load is held by the spool and any pressure in the compensator is vented to the tank core via an undercut in the spool and a hole drilled through the casting. The load-sense signal to the pump is decayed by a vent in the outlet. This enables the pump to stand-by at the prescribed pressure.

When the spool is actuated, the vent for the compensator closes and the pump flow is connected to the Q-Met Core via the metering notches on the spool. These notches are designed to provide specific flows at a margin pressure of 250 psi (for standard spools). The margin pressure is defined as a differential between the outlet of the pump and the load-sense port at the pump.

Pump flow into the Q-Met Core connects load pressure to the Q-Met Check. That pressure is shuttled downstream and the highest load pressure in the valve is returned to the load-sense control on the pump via a port in the outlet of the valve. The path is direct and no springs or poppets are compressed. This improves the speed of response and enables very low pressure stand-by with a bypass unloader.

When the load is connected to the Q-Reg Core, that pressure is communicated immediately via the induced-load check to the top of the compensator and, simultaneously, is shuttled downstream to the outlet. The highest pressure in the valve is then sent to the spring end of all the compensators. This arrangement maintains proportional flow to the operated sections during a pump overdemand situation. The exception is an induced load greater than the inlet pressure as dictated by the load-sense relief valve.

The work section compensator also acts as the transition check so that the load does not drift when the spool is shifted from the neutral to the power position.

Inlet

The inlet relief valve clips the pressure spikes which occur when a piston pump is being destroked or when a bypass unloader must start bypassing a majority of the flow quickly. This relief valve can also act as a secondary relief valve for back-up protection if the load-sense relief valve malfunctions. The inlet relief valve setting should always be 200-400 psi (17-28 bar) above the load-sense relief valve.

If the PC25 communicates with another loadsense valve, the load-sense signal from the other valve must be plumbed to a top port on the PC25. This connects it to the compensator logic system (Q-Reg Check) where it is compared with the other pressures in the valve. The highest pressure is then routed to the spring-end of all the compensators.

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