Hydraulic Elevator Equipment and Components
Hydraulic power train
A hydraulic elevator uses a power unit, pump, motor, tank, control valve, piping, jack, and plunger. Direct-acting jacks push the car directly; indirect systems use roping; telescopic jacks use multiple stages. The system includes a check valve, pressure relief valve, lowering valve, and often a rupture valve or pipe-burst valve. The relief valve protects the system from overpressure. The lowering valve controls descent. The plunger and cylinder require packing, a drip pan, and proper ventilation where oil can collect.
Worked example
A hydraulic unit needs 300 psi to lift its rated load. The pressure relief valve must be set to open at no more than 125% of that pressure: 300 × 1.25 = 375 psi. If the relief valve is set at 400 psi, it will not protect the system at the intended maximum. If it is set too low, the car may not lift rated load. The relief valve is a safety device, not a normal leveling control.
Traps that cost marks
Do not use the relief valve for routine lowering or leveling. Do not confuse the check valve, which prevents reverse flow, with the lowering valve, which controls down travel. Do not ignore oil temperature, foam, or low oil level; these affect leveling and valve operation. Remember that a rupture valve protects against uncontrolled descent if a pipe or hose fails.