Vestil HIPM series - Manual (Page 6)

6
HYDRAULIC OPERATIONFOR AC/DE
When the operator wants to raise the unit, he/she depresses the UP button. This starts the electric motor
which turns the hydraulic pump. Oil from the reservoir is drawn in through the suction filter and into the pump.
The pump delivers pressurized oil through a check valve before it enters the cylinders.
The function of the check valve is to allow the oil to flow in one direction, (towards the cylinders), and prevents
the flow of oil back into the pump circuit when the pump stops running. This holds the oil in the cylinders and will
maintain any particular barrel elevation, for extended periods of time.
If the load is excessive, and the UP button is still depressed, excessive pressure will build up in the circuit
between the pump and the cylinders. This forces the relief valve to unseat allowing the pump flow to circulate to
the reservoir preventing hydraulic or structural damage.
When the operator desires to lower the unit, he/she depresses the DOWN button. This energizes the
lowering solenoid valve coil, unseating the poppet valve and allowing oil return from the cylinders through the
pressure-compensated flow control valve, to the reservoir.
Releasing the DOWN button will de-energize the solenoid, closing the valve poppet. This and the check
valve prevents the oil from returning to the reservoir and the cylinders will stop retracting. The unit will maintain
that particular elevation until the operator chooses to move it once again.
Cartridge Valves
The lowering valve, as discussed above, is of cartridge construction and is virtually maintenance-free.
If there is a faulty operation, check Trouble Shooting Section. To clean the cartridge valve, follow this procedure:
1.) WARNING! Lower forks completely before removing cartridge valve.
2.) Use a sharp object to push poppet in from the bottom to open the valve.
3.) Repeat several times while valve is immersed in kerosene or mineral spirits. Blow dry.
4.) Blow compressed air through valve while holding the valve open as described in step 2.
5.) Inspect "o" rings and the teflon washer. If either shows nicks, tears, or cuts, replace.
6.) Reinstall. The valve should be tightened to approximately 20 ft. lbs.
Velocity Fuse
There is a brass velocity fuse with a stainless steel spring in the base of each cylinder (Item 10). In the
event of a hydraulic hose or fitting failure, the platform starts to lower at a fast rate. As soon as the descent speed
exceeds the preset speed, the Velocity Fuse will shut off the oil flow and the platform will remain nearly stationary
until pressure is re-applied after repairs are done. This safety feature reduces the possibility of accidental
personal injury or damage to the table or contents. If air is introduced into the system, the velocity fuse can lock
up even though no failure has occurred. To reset the velocity fuse just activate the pump by jogging the UP button.
Remove the load and cycle the unit several times to purge air.