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DB Pilot Operated Relief Valve – Engineering Details You Won't Find in a Catalog
How It Works – Three-Stage Operating Principle
A pilot-operated relief valve consists of a small pilot poppet and a large main poppet. Held closed by an adjustable spring, the pilot poppet stays shut when system pressure is below the set value. Equal pressure on both sides keeps the main poppet closed with no oil flow.
Once pressure hits the preset level, the pilot poppet opens slightly. A small flow of 1–2 L/min drains to tank, creating a pressure drop across the damping orifice. The main poppet then lifts gradually to divert excess flow.
Its gradual opening delivers a smooth pressure curve, with pressure rise under 5% at rated flow - far better than the 20–30% overshoot of direct-acting types.
Note: Flow forces affect main poppet operation despite pressure being set by the pilot spring. Our compensated main poppet with flow straightener effectively reduces this impact.
Real‑World Application Problems – And How We Solved Them
From thousands of field installations, we have identified five distinct issues that plague pilot operated relief valves.
Here is what goes wrong and what our DB pilot operated relief valve does differently.
Problem 1: Pressure rise with increasing flow
IssueThe valve cracks at 200 bar under low flow, but pressure climbs to 230 bar at 80 L/min when fully open. Excess system pressure may damage components.
Root causeOverly stiff main poppet spring or undersized damping orifice. Budget models omit flow force compensation.
Our solutionOur conical main poppet features a flow deflection shoulder. It redirects fluid to generate counteracting force and offset opening thrust. Pressure rise is controlled within 4–5% (max 7%), verified via NG10 tests up to 120 L/min.
Problem 2: Valve chatters or squeals under high flow
What happens – At flows above 60 L/min, the main poppet oscillates rapidly, producing a loud squeal and pressure spikes.
Root cause – The pilot stage and main stage resonate. The damping orifice is too large, or the pilot spring is mismatched.
Our solution – We specify the damping orifice diameter based on the viscosity grade of your oil. Standard orifice: 0.8 mm for ISO VG 46. For thicker oil (VG 68 or 100), we supply a 1.0 mm orifice. For thin oil (VG 22 or 32), a 0.6 mm orifice. Each valve is shipped with the correct orifice. We also add a small bleed notch on the main poppet to stabilize low‑flow operation.
Problem 3: Remote pressure control does not work smoothly
What happens – You connect a remote relief valve to port X (external pilot port). When you adjust the remote valve, the main pressure jumps in steps instead of changing smoothly. Or pressure drops to zero suddenly.
Root cause – The remote line contains air or has excessive volume. The pilot stage needs a restricted orifice to dampen remote signals.
Our solution – We include a 0.5 mm fixed orifice in the X port plug. This limits remote flow to 0.5 L/min, ensuring smooth adjustment. For long remote lines (over 5 meters), we also recommend a small accumulator near the valve – we can supply a 0.1L diaphragm accumulator for an extra cost.
Problem 4: The valve will not close after a pressure spike
What happens – A sudden pressure spike (e.g., from a directional valve closing) lifts the main poppet, but then the poppet stays open, dumping all pump flow to tank.
Root cause – The main poppet seats on a sharp edge. After a high‑velocity opening, the poppet wedges slightly off‑center and cannot reseat.
Our solution – We machine the main poppet seat with a 0.2 mm wide flat landing, not a sharp edge. The poppet is guided throughout its stroke by a long bearing surface. Even after a full 315 bar pop, it reseats reliably. We test each valve with three full‑pressure pop‑off cycles before shipping.
Technical Specifications – Detailed Parameters
| Parameter | NG6 (DBDS6) | NG10 (DBDS10) |
|---|---|---|
| Max pressure | 315 bar | 315 bar |
| Max flow (full open) | 60 L/min | 200 L/min |
| Pilot flow (control) | 1.5 L/min max | 2.5 L/min max |
| Pressure ranges (springs) | 10‑100, 20‑200, 30‑315 bar | Same |
| Pressure rise (closed to full flow) | ≤ 8% | ≤ 7% |
| Hysteresis | ≤ 3% | ≤ 3% |
| Repeatability | ±1.5% | ±1.5% |
| Damping orifice (std, VG46) | 0.8 mm | 0.8 mm |
| Remote control port (X) | G1/4 | G1/4 |
| Drain port (Y) – internal or external | External standard | External standard |
| Max back pressure on T (tank) | 30 bar | 30 bar |
| Weight | 1.8 kg | 4.2 kg |
Materials & Design Features That Matter
Main body – Forged steel for NG10, ductile cast iron for NG6. Both phosphated to 15 µm thickness.
Main poppet – 440C stainless steel, hardened to 60 HRC, lapped to seat.
Seat – Sintered bronze, pressed and finish‑machined. Replaceable.
Pilot poppet – Hardened tool steel, spherical tip, lapped to pilot seat.
Pilot spring – 54SiCr6, shot‑peened, preset, color‑coded by range.
Damping orifice – Removable stainless steel disc, laser‑drilled, marked with size.
Seals – NBR with backup rings. FKM, EPDM, or Viton available.
All adjustment screws have a friction washer and a locking nut with nylon insert (prevents vibration loosening). The hex key size is 5 mm for both sizes.
One-stop Cosmetic Hydraulic Factory in China
Founded in 1988, Shijiazhuang Laiye Import & Export trading Co,. Ltd belongs to Hebei Wendefu Hydraulic Technology Co., Ltd. is a high-tech enterprise focusing on R&D, production and sales of hydraulic valves, directional valves, pressure valves, flow valves, accessories, special components and other pressure valve components. The company has strong technical strength and processing capacity, and has hired a group of senior experts in the industry as senior consultants.
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