Service Manual H1 045/053/060/068 Closed Circuit Axial Piston Pumps Operation Pressure Limiter Valves (060/068 only) 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 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 low-pressure 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 overrunning or over-center. The pressure limiter is optional on H1 pumps. Pressure limiter valve To Servo
High Pressure
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, 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 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 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. Pressures marked on HPRV valve
10 | © Danfoss | April 2018
Mark
Pressure bar [psi]
15
150 [2175]
520L0958 | AX00000104en-000303
