Hydraulic power unit design

Reservoir

Tank volume sized for 5 to 8 times pump flow allowing fluid to settle in tank but re-circulate enough for stable temperature and keep clean. Actuator drain down and working volume changes must also be taken into account.

Made from painted mild steel or stainless / nyrosta steel.

Baffle plate

Separates return and supply lines allowing dirt and air to settle before reuse.

Tank access cover

Securely closed tank, designed so users cannot leave open. Used for maintenance access and cleaning only.

Air breather

Allows fluid volume in reservoir to change and filters air movement. If filling through the breather then new fluid should be pumped through a separate filter.

Suction line

Large diameter, short pipe for low fluid velocity. Pumps should have a positive head or be primed before first start. Often flexible pipe to isolate pump vibration from tank.

Suction filter

Can improve supply conditions but dangerous if not maintained as they can restrict pump supply.

Pump

Fixed or variable displacement pump supplies flow to circuit. Typically gear, vane or piston design depending on budget and performance. Isolate with rubber mountings to reduce noise.

Case drain line

Some pumps require case drain lines which must be adequately sized and primed with fluid before initial start up.

Bell housing and Coupling

A flexible drive coupling is required between the pump and motor to accommodate any misalignment or vibration. With some pumps the pump drive shafts move slightly with pressure so rigid location is not permitted.

Electric motor

Sized for maximum pump input power plus say 15% safety margin.

Pressure hose

Short flexible hose between pump and first component in circuit. Helps reduce noise and vibration. Allow pumps to move.

Pressure test point or gauge

For safety and maintenance a pressure gauge or test point are recommended

Pressure filter

Contamination causes over 90% of all failures. A pressure filter should stop contamination reaching components in the circuit. Include a bypass valve to stop clogging elements breaking and an indicator to say when elements need replacing.

Relief valve

Essential to protect the system against over pressurisation and potentially dangerous failures. Also used to unload system for pump startup or standby.

Isolation ball valve

Protect worker during maintenance and stop siphoning of fluid when items are changed or removed. Often lockable for extra security.

Filling point

Pump new fluid into the reservoir through the return line filter to ensure it's clean

Return line filter

Ideal for cleaning recirculated fluid. Bypass protects clogged filters from failing and visual or electrical indicators warn when elements need changing.

Anti siphon valve

Stops the backflow of fluid when valves in the circuit are removed for maintenance. Sometimes small holes are drilled above the fluid level inside the reservoir to break the siphon or screw fittings are provided to allow air breaks to be made.

Sight level gauge

Sight level gauges show the volume of fluid in the reservoir and are good early indicators of problems or leakage

Level switch

Level switches should remote visual warnings of low fluid and pump cut-out with very low fluid level. High fluid level warnings are also provided sometimes.

Temperature switch

Temperature warning and cut-out switches can be provided to ensure the system does not work outside its design limits

Immersion Heaters

Fluid immersion heaters often have built in thermostats to ensure the fluid stays above its minimum working temperature. This may be required before starting the pumps

Cooler

Return line or offline coolers prevent the tank temperature going above the design limits of the system.