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PUMP Brief TI-0014
Hydraulic Hydra ulic Pump Division
P1/PD Torque Limiter Guidance The Parker P1/PD series piston pumps for mobile and industrial open circuit applications offers a wide variety of control options. The torque limiter control is one of the most popular options.
AMT Schematic
The torque limiter control compares the pump swashplate position to the system pressure and adjusts the pump displacement to maintain a maximum shaft torque. Since most pumps are spinning at a constant input rpm, the unit will control the amount of horsepower the pump will demand. This is why these controls are often called horsepower limiting, or power limiting controls. There is a lot of confusion concerning the adjustment of this control as well as the adjustment range for each pump. This document provides detail on how to adjust the torque control cartridge. In addition, it provides important information on how to interpret the torque charts in the P1/PD product catalog.
Figure 1
The torque control is available with the AM control (pressure compensator with remote pressure port) on frame sizes 045 through 140 (model code call out AMT). With the AL control (load (load sense control) on frame sizes 045 and 060 (model code call out ALT).
And with the L0/L1 controls (load sense control) on frame sizes 075 through 140 (model code call out L0T).
To adjust the torque limiter 1. Loosen the jam nut by turning it clockwise 2. To decrease the torque setting turn the adjustment nut clockwise . To increase the torque setting, turn the adjustment nut counter clockwise . 3. Tighten the jam nut by turning it counter clockwise
The circuit diagrams for each control are provided in Figure 1, Figure 2 , and Figure 3. The torque limiter works by venting the compensator based in the physical cam position in the pump (Figure 4). The cartridge is threaded into the pump housing and interfaces with the pump swash plate through a mechanical feedback (1). This mechanical feedback is held against the swash plate with a lightweight spring (2). System pressure (or load sense pressure) is sensed through the elbow fitting (3). The pressure applies a force against the spool (4) and compresses the main spring (5). As the main spring compresses, the spool moves towards the pump swashplate until the cross drilling (6) in the spool moves outside of the sleeve (7) and allows the pressure to
relieve into the pump case, causing the pump to destroke. As the pump destrokes, the mechanical feedback (1) and sleeve (7) move towards the inside of the pump. Here, the swash plate is moving towards neutral allowing the spring (2) to push them out until the cross drilling (6) begins to close off. While the control is actively working in the torque curve, the spool (4) will continuously meter flow as pressure and swashplate position changes. The Parker P1/PD product catalog provides two generic torque curves. Figure 6 compares the displacement % to system pressure at 3 different settings. Figure 7 compares shaft torque to system pressure at the same three settings. Since these graphs are generic they cannot list a specific flow or torque. However, an estimated value can be found by taking the displacement of the unit used and calculating the flow at 1800 rpm, and also by calculating the torque of the unit at 4000 PSI. On P1/PD pumps, it is not recommended to set the torque limiter below 25% of maximum pump torque. Setting the torque limiter to a value below 25% will prevent the pump from achieving full stroke. It is recommended that a smaller displacement pump be selected if a unit is to be set below 25%.
P1-PD*** WITH TORQUE LIMITER TYPICAL PLACEMENT VS SYSTEM PRESSURE CURVE (1800 RPM) 120
Application Example Using a PD060 pump with maximum theoretical flow @ 1800 RPM is 28.5 GPM, the maximum theoretical torque @ 4000 psi would be 2330 in-lbs.
The prime mover has a HP rating of 30 HP @ 1800 RPM. This means that the maximum pump torque generated is 1050 in-lbs. The PD060 pump is the correct pump for the application since the prime mover torque rating is greater than 25% of the maximum theoretical pump torque (1050/2330 = 45%). Compensator setting is 3500 PSI. Using the Displacement vs. Pressure chart (Figure 8 ), it is possible to estimate that the unit will deliver full flow up to about 2000 PSI. At that point, the flow will decrease until compensator setting of 3500 is achieved. The flow before the pump compensates will be about 15.5 GPM. Figure 9 shows a standard torque curve at a % of torque setting. Using the above example of 45%, the nominal 50% setting curve can be used (purple graph line). Note that the torque curve bulges slightly above the nominal setting. This slight increase in torque is due to tolerance in the unit.
P1-PD*** WITH TORQUE LIMITER TYPICAL PLACEMENT VS SYSTEM PRESSURE CURVE (1800 RPM) 120 28.5 GPM
