Shijiazhuang Laiye Imort& Export Trading Co., Ltd. is one of the leading manufacturers and suppliers of dz pilot operated sequence valve substitute in China, also supports customized service. If you're going to wholesale high quality dz pilot operated sequence valve substitute made in China, welcome to get pricelist from our factory.
DZ Pilot Operated Sequence Valve Substitute
How DZ Pilot Operated Sequence Valve Works – No Fluff, Just Physics
The valve has a main spool and a pilot section. System pressure from the inlet (port P) feeds both the main spool and the pilot piston. The pilot piston is held closed by an adjustable spring. As long as inlet pressure stays below the spring setting, the main spool stays closed. No flow passes to the secondary port (A).
When pressure reaches the set point, the pilot piston opens slightly. This drains a small amount of oil from the main spool's end chamber, allowing the main spool to shift. Now flow goes from P to A – the second actuator gets oil.
The key detail: the spring does not directly balance the full flow pressure. It only sees a small pilot area. That means the valve can control high pressure and high flow with a small, precise spring. That is the "pilot operated" advantage.
One common misunderstanding: the sequence valve is not a relief valve. A relief valve opens to tank. A sequence valve opens to another working port. If you deadhead the secondary port, the valve will stay open and pressure will rise to the main system relief setting – potentially overloading the second actuator.
Real‑World Problems when using DZ Pilot Operated valve – And How We Solved Them
Over years of customer calls, we have seen three recurring issues with sequence valves. Here is what happens and what we changed in our Rexroth type sequence valve.
Problem 1: The sequence happens too early or too late.
Cause – The pilot spring is sensitive to oil temperature. Cold oil (high viscosity) increases pressure drop across the pilot orifice, fooling the valve into opening early. Hot oil (low viscosity) does the opposite.
Solution – We use a temperature‑compensated pilot orifice (a stainless steel disc with a precisely drilled hole). The effect is not perfect, but drift stays under ±8% from -10°C to +80°C. Most cheap alternatives drift ±20% or more.
Problem 2: The valve chatters when switching.
Cause – The pilot drain line (port Y) shares a return line with other valves. Back pressure on Y shifts the sequence setting.
Solution – Always run a dedicated drain line to tank. If that is impossible, order our version with an internal drain (port Y blocked). But note: internal drain raises the minimum pressure drop across the valve. We can advise based on your circuit.
Problem 3: The secondary actuator creeps before the sequence pressure is reached.
Cause – Internal leakage past the main spool. Standard spool clearances (0.015‑0.020 mm) allow some bypass.
Solution – Our DZ pilot sequence valve uses a lapped spool with clearance 0.006‑0.010 mm. Leakage is under 3 ml/min at 250 bar. For zero leakage, you need a poppet‑type sequence valve (different series) – but then you lose fine adjustability.
Technical Specifications – The Numbers You Actually Check
| Parameter | Value |
|---|---|
| Sizes | NG6 (CETOP 3) and NG10 (CETOP 7) |
| Max pressure | 315 bar (all ports) |
| Flow rating | NG6: up to 60 L/min; NG10: up to 160 L/min |
| Spring ranges | 5‑50, 10‑100, 20‑200, 30‑315 bar (other ranges on request) |
| Hysteresis | ≤ 4% of set pressure |
| Repeatability | ±2% |
| Pilot drain | External (standard) or internal (optional) |
| Temperature range | -20°C to +80°C (NBR); up to +120°C with FKM seals |
The body is forged steel for NG10, cast iron for NG6 – both phosphated.
All adjusting screws have a friction washer and brass‑tipped locknut.
Materials & Design Details That Matter
Spool – Hardened tool steel (58 HRC), DLC coated on the lands for wear resistance.
Spring – Shot‑peened 54SiCr6, preset to eliminate settling. Drift <3% after 200,000 cycles.
Seals – NBR standard, backup rings on all high‑pressure ports. FKM or HNBR available.
Pilot orifice – Removable, laser‑drilled stainless steel. You can clean or replace it without dismantling the whole valve.
Adjustment – Hex screw with 10 turns from fully closed to fully open. Each turn corresponds to roughly 10% of range. We provide a turn‑to‑pressure table with each valve.
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