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Shijiazhuang Laiye Imort& Export Trading Co., Ltd. is one of the leading manufacturers and suppliers of z2s6 sandwich pilot operated check valve in China, also supports customized service. If you're going to wholesale high quality z2s6 sandwich pilot operated check valve made in China, welcome to get pricelist from our factory.

Manufacturing – what we actually check

Our Xingtai line (Hebei Wendefu) produces these in batches of 200. Here is the real sequence:

Castings from our ISO 9001 foundry – we test one per mold for hardness and graphite structure.

Machining the sandwich body on a DMG Mori horizontal mill. The poppet seat is bored and then roll‑finished – no cutting marks.

The poppet is CNC ground, then lapped on a cast iron plate with diamond paste. Each poppet is vacuum‑tested against its seat before assembly.

The pilot piston and bore are matched by air gauging. Clearance 0.008‑0.012 mm – tight enough to prevent oil bypass, loose enough to slide freely.

We assemble each Z2S6 pilot operated check valve and test on a rig that cycles the pilot pressure 1000 times while measuring seat leakage every 100 cycles. Test takes 20 minutes per valve. We reject any that leak more than 3.5 ml/min at any point.

Finally we stamp the pilot ratio on the body and pack with a printed test report.

A QR code on the side gives you the full test curve – not just a pass/fail.

Where to use this valve (and typical mistakes)

This sandwich plate check valve is common in:

Plastic injection machines – holding the mold clamp while core pulls move

Vertical cylinder circuits (presses, lifts) – preventing drop when the directional valve centers

Hydraulic clamping systems – maintaining pressure without pump running

The most common mistake: installing the valve backwards. The pilot port X must be connected to the directional valve's working port that sees pressure when you want to open the check. For a double‑acting cylinder: if you want to lock the rod side, the pilot signal must come from the cap side line. Read our orientation guide (available as PDF).

Another mistake: using this valve without a downstream pressure relief. If the load can create pressure higher than the pilot ratio times pilot pressure, the check may crack open unintentionally. For overrunning loads, add a restrictor in the pilot line.

Typical problems we see from the field

Problem: Cylinder drifts down even with valve installed.

Check: often the pilot signal port X is connected to tank when the directional valve is in neutral. That is correct. But if the directional valve spool leaks internally, pressure can build in the pilot line and crack the check open. Solution: add a small restrictor in the pilot line to dampen pressure spikes. We include a 0.8 mm orifice plug with every 10 valves – ask for it.

Problem: Valve does not open even with pilot pressure.

Check: pilot pressure might be present but blocked by a stuck pilot piston. Remove the valve and inspect the piston bore. If you see varnish, your oil is oxidized. Clean with solvent. For severe cases, order a valve with the PTFE piston guide (standard on our version – so unlikely).

Problem: Noise when closing.

The poppet slams shut when pilot pressure drops rapidly. That is normal. If the noise is excessive, add a small check‑orifice in the pilot drain line to slow the closing. Not a defect.