Installing, Tuning and Troubleshooting Control Valves in Press Systems

Installing Control Valves: Preparation, Pipework and Flushing

The majority of control valve faults begin before the valve is ever energised. New pipework carries swarf, weld spatter, mill scale and sealed-in air, and any of these will damage a spool or seat within minutes. A valve installed on a freshly welded circuit without a flushing procedure will usually fail, and the failure is blamed on the valve rather than on the installation.

Flush the circuit before the valve goes in. Connect a flushing rig or a suitable pump and reservoir, circulate with the actual working oil at operating temperature, and pass the flow through a temporary filter of about 10 micron rated at full circuit flow. Continue until the return filter stays clean, then drain the circuit and remove the temporary filter. Also check pipework alignment before fitting: the mounting bolts should pass freely by hand and the face should be flat within tolerance. A forced, misaligned valve loads the bore and binds in one direction only.

Mounting Orientation, Support and Pipe Routing

Most cartridge and manifold valves are weight sensitive. A solenoid-operated spool valve hung on soft tube lines will resonate, and a light valve that vibrates will chatter, wear its guide and eventually stick. Support the valve on its own mounting surface or a rigid bracket, and clamp the rigid pipework so the valve body carries no bending load from the tube.

Orientation matters in specific ways. Pilot operated valves with internal drain lines must be mounted so the drain cannot be trapped, because trapped pilot drain pressure prevents the main stage from shifting. Sequence and counterbalance valves with an external drain should sit above the reservoir oil level and be piped back to tank without restriction. Check the data sheet for permitted mounting attitude before fitting a cartridge valve vertically. Route return lines to the tank by a short, straight path, and fit gauges at the working line rather than at the pump.

Solenoid and Coil Selection for Press Duty

Coil selection is straightforward once three questions are answered: what voltage is available, what current the driver can supply, and how often the valve switches. 24 VDC is the usual industrial choice because the cabinet can then carry the same safety devices as the rest of the machine. A 12 VDC coil draws roughly twice the current of a 24 VDC coil of the same power, which matters when several solenoids share one supply.

Check the coil duty data. Coils marked continuous duty can stay energised for the whole cycle, while a valve holding a spool energised for hours will run warm and eventually fail. A duty figure of 75 percent on means the coil must not be energised for longer than three quarters of the cycle. Protection class IP65 or higher is appropriate for areas with coolant, washdown or swarf, and a plug connector simplifies replacement. Manual override is worth specifying on any valve that controls a moving load, because a plunger override lets a technician shift the spool after a failed coil.

Energising and De-Energising Valve Behaviour

Every valve has a defined behaviour when power is applied and removed, and that behaviour is often the whole safety case. A spring-offset solenoid valve returns to its default position when the coil is de-energised, so a press can be made safe by removing power. A solenoid with no spring return must be backed by a mechanical or hydraulic arrangement that fails to a safe state.

Spring offset means the coil pushes the spool open and the spring closes it, or the reverse. Check this against the required safe state before wiring. On a vertical press the safe state is normally ram held or lowered under control, never ram free to fall. A pilot operated valve with spring return can hold position on pilot pressure alone, so it stays workable during a mains power failure provided the pilot supply remains.

Setting Flow and Pressure: Adjustment Procedures

Set the pressure relief valve first, and set it against the machine rather than on the bench. Connect a calibrated gauge to the working line, raise system pressure slowly with the actuator at its intended stop position, and adjust the relief until it reads the target value, normally 10 percent above working pressure and never above the lowest rated component, often the cylinder or the frame. Lock the adjuster and mark the position with paint.

Then set the flow control valve with the load in place. Run the ram to the working position, adjust the metering valve until the observed speed matches the specified work speed, and record the adjuster position. Repeat once the oil temperature has stabilised, because a valve set cold will run faster when the oil thins. For close-tolerance press fits, fit a pressure and position sensor and use closed-loop control. Finally, set the counterbalance to hold the ram at the required back pressure, lower the ram slowly and confirm there is no drift, then set the sequence valve by loading the system.

Diagnosing Common Valve Symptoms

Most press problems arrive as press behaviour rather than as valve faults: the ram stalls, hunts, will not hold, or bangs. Reading the symptom correctly narrows the search. Start by separating an electrical fault from a hydraulic one, by checking voltage at the connector under load and by confirming pilot supply pressure is present when the valve fails to shift.

Spool Contamination, Seals and Stuck Poppets

Spool sticking is nearly always a contamination problem. Particles of 20 to 40 micron entering the metering lands hold the spool slightly off-centre, and the uneven force on the guide produces a binding action that worsens with each stroke. Filter the system to about 10 to 25 micron for the working pressure range, replace the element at the scheduled interval rather than when it looks dirty, and fit a filter with a visible clogging indicator so a restriction is caught before it starves the pilot circuit.

Also check the suction side. A blocked strainer or a cracked suction hose draws air into the pump, and aerated oil causes cavitation at the cylinder, unstable flow and a valve that appears to hunt; a vacuum gauge at the pump inlet is the quickest test. Poppet valves fail differently: a poppet that will not seat leaves the line open, so the circuit cannot hold pressure and the pump runs against a leak. Look for scoring on the seat face, corrosion product, or a damaged spring. Check seals on every strip-down, including the cylinder rod seal, which is often mistaken for a valve fault.

Inspection, Maintenance and Safe Isolation

Put valve maintenance on a written schedule rather than leaving it to failure. The useful checks are simple: listen for chatter, feel for heat at the valve body, watch the pilot filter indicator, and confirm oil temperature and cleanliness at the sample point. Record the readings, because a slow trend in pilot filter differential pressure or particle count predicts failure long before the press stops. At planned shutdowns, clean solenoid valves where access allows, check the spool for wear at the lands, and fit new seals.

No valve is opened under pressure. Before any work, switch off and lock out the main isolator, close isolation valves upstream and downstream of the valve, and mechanically secure the ram so stored energy cannot move it; a vertical press can fall under the weight of the moving slide alone. Bleed trapped lines through designated bleed points and confirm gauges read zero. Do not rely on the solenoid being de-energised or on the relief valve to hold, because a failed coil is the situation you are working in. Drain the section into a clean container, plug the lines, and after reassembly leak check and function test a full stroke.

Frequently Asked Questions

Do I need to flush a hydraulic press circuit before installing a control valve?

Yes. New pipework carries swarf, weld spatter, mill scale and air, and these damage spool lands and seats quickly. Flush the circuit with the working oil at operating temperature through a fine filter, check that the filter stays clean, then drain the circuit and remove the temporary filter before fitting the valve.

Why will a solenoid operated control valve not shift even though the coil is powered?

Power at the connector does not guarantee that the spool moves. Check pilot supply pressure, since pilot operated valves need a minimum pilot flow, and check the pilot filter for blockage. Confirm voltage at the coil under load, verify coil resistance, and inspect the spool for corrosion or debris.

How often should a press control valve be inspected?

Per shift, check the filter indicators and listen for chatter or unusual noise. Sample the oil for particle count monthly, clean and inspect the spool every six to twelve months, replace seals whenever the valve is stripped, and verify relief and counterbalance settings every six months and after any adjustment.

What is the correct way to set the relief valve on a hydraulic press?

Set it against the machine with a calibrated gauge on the working line, at about 10 percent above working pressure and never above the lowest rated component such as the cylinder or the frame. Adjust slowly while the pressure rises, lock the adjuster and mark the position.