Pressure Limiter Valves
Pressure limiter valves provide system pressure protection by compensating the pump swash plate
position when the set pressure of the valve is reached. A pressure limiter is a non-dissipative (non heat
generating) pressure regulating system.
Each side of the transmission loop has a dedicated pressure limiter valve that is set independently. A
pump configured with pressure limiter must have pressure limiters on both sides of the system pressure
loop. The pump order code allows for different pressure settings to be used at each system port.
The pressure limiter setting is the maximum differential pressure between the high and low loops. When
the pressure limiter setting is reached, the valve ports oil to the low-pressure side of the servo piston. The
change in servo differential pressure rapidly reduces pump displacement. Fluid flow from the valve
continues until the resulting drop in pump displacement causes system pressure to fall below the
pressure limiter setting.
An active pressure limiter destrokes a pump to near neutral when the load is in a stalled condition. The
pump swash-plate moves in either direction necessary to regulate the system pressure, including into
stroke (overrunning) or over-center (winch payout).
The pressure limiter is optional on H1 pumps (except H1T 045/053 tandem pumps).
Pressure Limiter Sectional View
High Pressure Relief Valve (HPRV) and Charge Check Valve
All H1 pumps have a combination high pressure relief and charge check valve. The high pressure relief
function is a dissipative (heat generating) pressure control valve for the purpose of limiting excessive
system pressures. The charge check function replenishes the low pressure side of the working loop with
charge oil.
Each side of the transmission loop has a dedicated HPRV valve that is non-adjustable with a factory set
pressure. When system pressure exceeds the factory setting of the valve, oil is passed from the high
pressure system loop, into the charge gallery, and into the low pressure system loop via the charge
check.
The pump may have different pressure settings to be used at each system port. When an HPRV valve is
used in conjunction with a pressure limiter, the HPRV valve is always factory set above the setting of the
pressure limiter. The system pressure shown in the order code for pumps with only HPRV is the HPRV
setting.
Service Manual
H1P 069—H1P 250 Axial Piston Single Pumps
Operation
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©
Danfoss | September 2020
AX152886482551en-000504