Pressure Relief Valves for Direct Acting and Pilot Operated Hydraulic Reliefs

What a Relief Valve Does

Every hydraulic circuit needs a pressure limit. When the pressure reaches the relief setting, the valve opens and diverts flow to tank. When the pressure falls, it closes again. Without one, a stalled cylinder or blocked line would push the pressure up until something breaks.

Direct Acting or Pilot Operated?

• Direct acting: a spring holds a poppet or ball on its seat. These valves are simple, compact and very fast to respond, which makes them ideal for small flows, cartridges and shock protection.
• Pilot operated: a small pilot relief controls a larger main stage. The pressure stays flatter across a wide range of flow, so these are the usual choice for main system reliefs on bigger power units.

Many pilot-operated reliefs have a vent port. Fit a solenoid valve to the vent and the relief can unload the pump on command, letting it idle at low pressure between cycles.

Cracking Pressure and Override

A relief valve does not snap fully open at one exact pressure. It starts to open at the cracking pressure and needs a little more to pass full flow. The difference is called override, and direct acting valves usually have more of it than pilot operated ones. Always size the valve for the full pump flow, not just the setting.

Where Relief Valves Sit

• Main system relief: right after the pump, protecting the whole circuit.
• Port reliefs: on the individual work ports of mobile valves, protecting each function.
• Cross port reliefs: across the two lines of a hydraulic motor, cushioning sudden stops.
• Thermal reliefs: on trapped lines that can build pressure as the oil warms in the sun.

In compressed air systems, safety valves do a similar job on receivers and lines.

Signs of Trouble

• The system will not reach full pressure, often because of a worn seat or a weak spring.
• The oil runs hot, because the relief is passing flow most of the time.
• The valve chatters or squeals, usually from wear, dirt or the wrong size.
• The pressure creeps above the setting as flow rises, a sign of too much override.

A hot relief valve body during normal running is a clue that oil is being dumped and energy wasted.

Keep the Setting Honest

• Choose lockable or tamper proof adjusters where operators might be tempted to wind them in.
• Record the setting on the valve tag and the circuit drawing.
• Check the setting with an accurate gauge at each service.
• Never set the relief above the rating of the weakest part in the circuit.

Pressure Relief Valves Specifications to Check

• Pressure range and setting
• Maximum flow
• Direct acting or pilot operated, and any vent port
• Mounting: cartridge cavity, inline thread, subplate or modular
• Adjustment type: screw, knob or tamper proof
• Seal material and fluid type

Why Buy From TSA Hydraulics Engineering

As a pressure relief valves supplier, we match the pressure range, flow and cavity, so the new valve protects the system the way the old one did. You get clear prices in AUD, OEM or equivalent options, and help sourcing pressure relief valves replacement parts such as cartridges, springs and seal kits. We tell you upfront whether a valve is genuine or an equivalent.