Mts Model 293-22 Hydraulic Service Manifold Manuel d'utilisateur télécharger pdf (Page 20)

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.

About HSM Pilot Pressure

The HSM is equipped with a hydraulic circuit which provides separately filtered fluid at HPU pressure to

operate the pilot stage of multistage servovalves. This portion of the HSM operates automatically and

requires only routine filter maintenance.

Note:

Turning pressure on and off, or changing between low and high output pressure, does not affect

the pilot pressure output. Pilot pressure is always present, as long as pressure is available from the

HPU. The pilot circuit takes time to bleed down after high pressure is removed from the HSM.

HSM Accumulators

The pressure, return, and pilot pressure accumulators reduce pressure and flow fluctuations caused by

changing system demands. When the HPS is located some distance from the actuator, the flow and

pressure of the hydraulic fluid may be inadequate at certain frequencies.

The type and frequency of the servovalve command signal affects the efficiency of the accumulator. Square

waves cause a greater demand than sine or ramp signals. At low frequencies, fluid flow in the lines can

stop completely and fluid inertia can become an operational factor.

The pressure accumulator reduces the inertia and line restriction considerations. When the servovalve

opens and line pressure begins to drop, the accumulator supplies part of the fluid volume to help maintain

line pressure. Then, when the servovalve closes, the accumulator recharges, causing fluid in the lines to

remain in motion.

An accumulator in the return line reduces pulsing caused by the varying amounts of fluid being discharged

into the lines as the actuator moves. Movement of hoses or "hammering" of hard lines is thus reduced.

HSM Slow Turn-On

The control manifold contains the slow turn-on accumulator. The fixed control circuit inlet orifice, and the

variable low-pressure adjustment orifice affects the rate at which the control circuit operates. When the

low-pressure solenoid is energized, hydraulic fluid is allowed to flow through the control circuit inlet orifice.

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Mts Model 293-22 Hydraulic Service Manifold Manuel d'utilisateur Page 20