Danfoss Series 90, Техническая информация

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Multi-Function Valves
Overpressure protection
The Series 90 pumps are designed with a sequenced pressure limiting system and high pressure relief
valves. When the preset pressure is reached, the pressure limiter system acts to rapidly de-stroke the
pump to limit the system pressure. For unusually rapid load application, the high pressure relief valve is
also available to limit the pressure level. The pressure limiter sensing valve acts as the pilot for the relief
valve spool, such that the relief valve is sequenced to operate above the pressure limiter level.
Both the pressure limiter sensing valves and relief valves are built into the multi-function valves located
in the pump endcap. The sequenced pressure limiter/high pressure relief valve system in the Series 90
provides an advanced design of overpressure protection.
The pressure limiter avoids system overheating associated with relief valves and the sequenced relief
valves are available to limit pressure spikes which exist in severe operating conditions.
Because the relief valves open only during extremely fast pressure spike conditions, heat generation is
minimized during the short time that they might be open. For some applications, such as dual path
vehicles, the pressure limiter function may be defeated such that only the relief valve function remains.
The relief response is approximately 20 ms whether used with or without the pressure limiter function.
Pressure limiting function
When set pressure is exceeded, the pressure sensing valve (A) flows oil through passage (B) and across an
orifice in the control spool raising pressure on the servo which was at low pressure. Servo pressure relief
valves (C) limit servo pressure to appropriate levels. The pressure limiter action cancels the input
command of the displacement control and tends to equalize servo pressure. Swashplate moments assist
to change the displacement as required to maintain system pressure at the set point. The HPRV is always
set 30 bar above the pressure limiter setting.
HPRVs are factory set at a low flow condition. Any application or operating condition which leads to
elevated HPRV flow will cause a pressure rise with flow above a valve setting. Consult factory for
application review. Excessive operation of the HPRV will generate heat in the closed loop and may cause
damage to the internal components of the pump.
Multifunction valve, pressure limiter, pressure regulation, option 1
M
B
L2
M2
M1
M4
M5
M3
A
S
Charge
pressure
relief valve
Multifunction valve
Multifunction valve
To control
Servo piston
Servo piston
Port A
Port B
C
Bypass hex
adjustment
P102 007E
Servo pressure
relief valves
A
B
Technical Information Series 90 Axial Piston Pumps
Features and Options
40 520L0603 • Rev 0804 • March 2016