Rev. 9/25/2017
HDC-450, MANUAL
Copyright 2017 Vestil Manufacturing Corp. Page 10 of 26
Hydraulic System - 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, 6, 7, &
9)
, 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 automatically adjusts 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. However, if the load weighs too much (weight exceeds the
capacity), then a pressure relief valve opens. When the relief valve is open, oil flows back into the reservoir rather than
to the cylinder. The arm will not rise until the weight of the load is either equal to
or less than the capacity of the lifter.
Lower the pivot arm by pressing the release lever (see 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 has been in use for a while, 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 port on the cylinder and insert the free end of the hose into the
reservoir.
4. Pump the foot pedal several times. Pockets of air will escape as oil flows from the hose and 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.
1
1
/
2
in. x 18in.
displacement
cylinder with
internal
velocity fuse
Pressure compensated
flow control; 1GPM
Pressure
check valve
Adj.
pressure
relief valve
Pressure
check
valve
Lowering valve
2-speed
foot pump
Hydraulic circuit diagram (foot pump)
