4
Hydraulic System Operation
Hydraulic Systems
There are three types of Hydraulic Systems: Open
center, Closed Center (Pressure Compensated), and
Closed Center Load Sensing (Flow and Pressure
Compensated).
Open Center Systems
In an Open Center System, the hydraulic pump puts out
a constant flow. If the Pump puts out more than the
Motor can use, a portion of the oil must be bypassed
around the Motor. The Bleeder Bypass Screw allows the
fluid to bypass around the Motor. When the oil is
bypassed around a loop and does no work, the energy
put into it by the Pump turns into heat. Therefore, this
should only be used on smaller Open Center Systems
where the amount of oil that must be bypassed is
minimal.
Closed Center (Pressure Compensated) Systems
Closed Center (Pressure Compensated) Systems have a
Variable Displacement Pump that will deliver flow at the
necessary rate to maintain a specified pressure. The
Flow Control Valve should be installed at the Motor Inlet
to control the flow according to the Model requirements.
Closed Center Load Sensing Systems (Flow and
Pressure Compensating)
The Closed Center Flow Compensated System is a
variation of the Pressure Compensated System,
designed primarily for more efficient operation and the
generation of less heat. It works on the principle of
maintaining a constant pressure drop from the pump to
the working port of the Selector Valve. Any variation in
demand at the Motor will cause a change in flow. The
system senses this change in flow due to the change in
pressure drop across the Valve and causes the pump to
compensate by varying the Pump flow
Do not bypass oil. Use a Flow Control at the Motor
Inlet to control the flow and speed of the motor.
Hydraulic Oil
The specifications for the Hydraulic-Driven Pressure
Washer where compiled using Mobil DTE-26 hydraulic
oil at a temperature of 140° F [60° C]. Using other type
of oil and different temperatures will result in different
flow requirements to replicate these Pressure Washer
performance specifications. These specifications are a
guide for initial start-up.
Pump Repair Instructions
Plunger Replacement.
1. Using a metric allen wrench, remove the Socket
Head Cap Screws securing the Pump Head to the
Pump Body (See Figure 3).
2. While turning the Crankshaft, use two screwdrivers to
carefully pry between the Pump Head and Pump
Body to remove the Pump Head (See Figure 4).
3. Remove the plunger Retaining Nut and the Plunger
Retaining Nut Washer (See Figures 5).
4. Slide the Plungers off the Piston Guides (See
Figure 5).
5. Remove and discard the O-rings (See Figure 5).
6. Remove the Slinger Ring (See Figure 5).
Figure 3
Remove
Socket Head Cap
Screws
Figure 4
While turning the
crankshaft, use
screwdrivers to pry
the pump head off.
Change the oil after 40 hours of break-in operation.
Thereafter, change the oil every year or 500 hours,
whichever comes first.
Care of the Pump
After each use, flush the pump with a neutralizing
solution for the liquid pumped. Follow this with a clear
water rinse. For storage under freezing conditions, flush
the pump with a 50/50 solution of automotive-type
antifreeze and water.
Bypass Operation
During Bypass Operation (when water is diverted back to
the pump inlet side) a temperature rise occurs. A
Thermal Relief Valve is provided to maintain the
maximum water temperature at 145° F [63° C].
