Table of Contents Rev. 10/13/2022 HDC-450, MANUAL
Table of Contents Copyright 2022 Vestil Manufacturing Co. Page 8 of 24
HYDRAULIC SYSTEM - AUTOSHIFTER FOOT PUMP
Your new lift equipment includes a two-
speed pump that automatically shifts between
speeds based on the output pressure of the
hydraulic system. The pump extends and
retracts the hydraulic cylinder (part number 99-
021-904-001 in the exploded parts drawings on
pages 4-7), which raises or lowers the pivot arm
and drum saddle/carriage. Internal features of
the pump include primary pressure relief and
pressure compensated return flow mechanisms,
an integrated lowering valve, and an auto-
shifting valve assembly. The pump also utilizes
replaceable sleeve bearings, valve
components, and seals to simplify
maintenance requirements and maximize
service life.
Operation
Pump speed is automatically adjusted based on the output pressure of the hydraulic system. For example,
when the drum saddle is unloaded, pressure in the hydraulic system is low. Under these conditions, the pump
operates in high speed mode. Each stroke of the foot pedal pumps approximately 1.2 cubic inches of oil and the
pivot arm (and drum) rises rapidly. When a drum is connected to the drum saddle, hydraulic system pressure
increases as the drum lifts off of the ground. At pressures in the range of 800-1000 psi the pump automatically shifts
to low speed mode. In low speed mode, each stroke pumps approximately 0.44 cubic inches of oil. Less effort is
required to move the pedal when the pump is in low speed mode, by the cylinder extends much more slowly,
i.e. the pedal has to be pumped many more times to raise the arm.
The pivot arm rises with each stroke of the foot pedal. If too much weight is applied to the saddle, i.e. weight
exceeding the capacity, a pressure relief valve opens and directs oil back into the reservoir rather than to the
cylinder. As a result, the arm will not rise until the weight of the load is either equal to or less than the capacity of
the lifter.
To lower the pivot arm, press the release lever. See Autoshifter item no. 21 on pages 9 & 10). As the arm
lowers, a pressure compensated flow control valve ensures that it lowers at a controlled rate. Do not increase the
pressure relief setting more than necessary, i.e. be sure that you do not exceed the pressure rating of the
components in the hydraulic system.
Purging Air from the Pump
Whether your pump is new or used, air probably is trapped inside the pump and must be removed. When air is
present in the hydraulic system, you might notice that the foot pedal feels spongy. To remove air from the system:
1. Lower the pivot arm.
2. Remove the cover from the modular power unit and unscrew fill plug from the oil reservoir.
3. Disconnect the hydraulic hose from the cylinder port; insert the free end of the hose into the reservoir.
4. Pump the foot pedal several times. Pay close attention to the stream of oil flowing from the hose. Pockets
of air will escape as oil flows into the reservoir.
5. Once air is no longer present, reconnect the pump to the cylinder by reattaching the hydraulic hose to the
cylinder port. Check all of the hydraulic lines for oil leaks; then return the table to service.
6. Although air has been removed from the pump, air could still be trapped in the cylinder. The next
procedure explains how to remove air from the cylinder.
Purging air from the cylinder:
A bleeder screw is located at the top of the cylinder. The bleed screw includes a hose fitting to allow
attachment of a small diameter hose. By attaching a hose to the screw, any oil that escapes during the bleeding
process can be directed into a container for proper disposal. To bleed air from the cylinder:
1. Lower the pivot arm.
2. Pump the foot pedal once.
3. Carefully open the bleeder screw. The pressure in the system generated by pumping the pedal causes air
(and oil) to flow out of the bleeder screw. Pressure will drop as air and oil flow from the cylinder. To pressurize the
system, close the bleed screw and pump the pedal once. Open the bleeder screw again to allow more trapped
air to escape.
4. Repeat step 3 until air is completely removed from the cylinder, i.e. only oil flows from the bleeder screw.
5. Check all of the hydraulic lines for oil leaks.
6. Return the unit to service.
2
displacement
cylinder with
internal
flow control; 1GPM
check valve
pressure
check
valve
foot pump
Hydraulic circuit diagram (foot pump)
