MTS Hydraulic Service Manifold Model 293-12B - Manual (Page 20)

HSM Fluid Flow
Hydraulic fluid from the HPU enters the HSM at the pressure in port. It passes through an inlet check valve
and a filter. After filtration, part of the fluid is channeled to the pilot pressure circuit. The rest of the fluid
passes through a control manifold, fills the pressure accumulator, passes through the control manifold,
and exits the HSM to an actuator/servovalve through the pressure out port.
Return fluid from the actuator enters the return in port. It flows past the return accumulator and exits to the
HPU through the return out port. Drain ports provide a path for collecting excess fluid and returning it to
the HPU.
HSM Filtering
Fluid passes through the main pressure filter with a wire-mesh cleanable element. An inlet check valve
provides backflow protection for the main filter element when supply pressure drops as the HPU is turned
off. A pilot pressure filter provides 3 μ (absolute) filtration with a visual indicator that shows when the filter
is dirty.
HSM Pressure Control
The control manifold supplies hydraulic pressure to the servovalve and controls whether the pressure is
high or low at the HSM pressure output ports. High-pressure output is typically maintained at 21 MPa
(3000 psi). A gage on the HSM indicates output pressure.
The HSM is in the off-pressure mode when fluid flow is blocked by the main control valve. When low-pressure
solenoid SOL1 is energized, a restricted flow is ported to the slow turn-on accumulator, which begins to
charge. Pressure rises and is applied to the main control valve, causing it to open and port fluid to the
pressure out port. The main control valve opens and closes automatically to maintain the low pressure
level set by the low-pressure adjustment, stabilizing the HSM in low-pressure mode.
When high-pressure solenoid SOL2 energizes, pressure in the control circuit rises and is applied to the
main control valve, causing it to open completely and remain open. The HSM is now in high pressure
mode. De-energizing SOL2 allows pressure to bleed off.
The main control valve closes until the low-pressure setting is reached. The HSM is now in low-pressure
mode. De-energizing the low-pressure solenoid disconnects HPS pressure from the control circuit. The
control circuit is now connected to the drain line, and pressure drops rapidly. As control circuit pressure
drops, downstream pressure and a control spring fully close the main control valve. The HSM returns to
the pressure-off mode.
20 | Series 293 Hydraulic Service Manifold Product Information
Introduction