// Catalogue

Servo Valves for Fast, Precise Closed-Loop Hydraulic Control

Servo valves are the most precise hydraulic control valves. They turn a small electrical current into fast, accurate control of flow and pressure in closed loop systems. TSA Hydraulics Engineering supplies them within the Servo & Proportional family of our Valves range.

Fit a new servo valve to dirty oil and you have bought a very expensive filter. These valves have clearances measured in microns, and they fail quickly if particles get in. So before we match a factory original or an equivalent, we ask about your filtration as well as the model code, rated current and flow.

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// Buying guide

How a Servo Valve Works

Most traditional servo valves have two stages:

A torque motor receives a small current, often just a few milliamps.
The torque motor moves a pilot stage, either a flapper between two nozzles or a jet pipe, which creates a pressure difference.
That pressure difference moves the main spool, which controls the full flow.
A feedback spring or wire returns the spool’s position to the torque motor, so the spool settles exactly where the signal asks.

Direct drive servo valves skip the pilot stage. They use a strong linear motor with onboard electronics to move the spool directly.

Types of Servo Valve

Flapper nozzle: the classic design. Very fast, but sensitive to dirt.
Jet pipe: more tolerant of contamination, and popular in industrial and heavy duty use.
Direct drive: no pilot flow, simpler wiring and less sensitivity to supply pressure.
Three stage: a servo valve driving a larger main stage for very high flows.

Performance Figures That Matter

Rated flow: usually quoted at a 70 bar pressure drop across the valve.
Rated current or signal: for example plus or minus 10 mA or 40 mA, or a voltage for valves with onboard electronics.
Frequency response: how fast the valve follows a changing signal, shown in hertz.
Hysteresis and threshold: how closely the valve repeats its position.
Null leakage: flow lost internally when the spool is centred, which adds heat.

Match all of these when choosing a replacement, not just the size and mounting.

Protecting a Servo Valve

Fit a fine filter, often 3 to 10 micron, in the pressure line just before the valve.
Flush the system with a flushing plate fitted before installing a new valve.
Keep the protective cover plate on until the moment you fit the valve.
Monitor oil cleanliness regularly, aiming for ISO 4406 code 16/14/11 or better.

Signs of Trouble

The actuator drifts when the command is zero, a sign of null shift.
The system hunts or oscillates.
Response becomes sluggish.
The oil runs hotter than usual, which can point to high internal leakage.

Many of these trace back to contamination, so check the oil and filters first.

Servo Valves or Proportional Valves?

Servo valves give the best speed and accuracy, but they need very clean oil and careful setup. For many presses and mobile machines, modern proportional valves with onboard electronics now come close enough, at a lower cost and with more tolerance for dirt.

Servo Valves Specifications to Check

Rated flow at the stated pressure drop
Rated current or command signal, and the connector
Pilot design: flapper nozzle, jet pipe or direct drive
Mounting pattern and port size
Frequency response and null leakage
Maximum operating pressure

Why Buy From TSA Hydraulics Engineering

As a servo valves supplier, we match the rated flow, current and pilot design, not just the bolt pattern. You get clear prices in AUD, OEM or equivalent options, and help sourcing servo valves replacement parts such as filters, seal kits and flushing plates. We tell you upfront whether a valve is genuine or an equivalent.

// FAQs