Pressure Limiter Valves
Pressure limiter valves provide system pressure protection by compensating the pump swashplate
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 (and each section of the tandem pump) has a dedicated pressure
limiter valve that is set independently. Each system port may have a different pressure limiter setting.
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 lowpressure side of the servo piston. The
change in pressure across the servo 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 the pump to near neutral when the load is in a stalled condition. The
pump swashplate moves in either direction necessary to regulate the system pressure, including
increasing stroke when over-running or over-center.
The pressure limiter is optional on H1 pumps.
069/078/089/100 Single Pumps
115/130/147/165/210/250 Single Pumps
High Pressure Relief Valve (HPRV) and Charge Check
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 non-adjustable, factory-set HPRV valve.
When system pressure exceeds the factory setting of the valve, it passes oil from the high pressure
system loop into the charge gallery and the low pressure system loop via the charge check.
The pump may have different pressure settings 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. The
system pressure shown in the order code for pumps with both pressure limiter and HPRV is the pressure
limiter setting.
HPRVs are set at low flow condition. Any application or operating condition which leads to elevated HPRV
flow will cause a pressure rise with flow above the valve setting. Consult factory for application.
Service Manual
H1 Pumps 069/078, 089/100, 115/130, 147/165, 210/250
Operation
©
Danfoss | May 2018
520L0848 | AX00000087en-US0308 | 11
