DA Series Pilot Operated Relief Valve

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

How the DA series is built
The DA series is a pilot operated relief valve constructed from a single-piece iron casting. The body is machined from a solid casting rather than assembled from multiple welded or bolted components. This construction method eliminates weak points at joints and ensures that the internal flow passages and spool bores are aligned precisely during machining. The body casting is inspected for porosity and surface defects before it enters the machining line. If a casting shows signs of defects, it is rejected before any machining time is spent on it.

Pilot stage and main stage
The valve uses a two-stage design. The pilot stage is a small spool assembly located on the top of the valve body. It is spring-loaded and can be adjusted by turning the manual knob. The main stage is a larger spool that sits in the main body and handles the full flow of the system. The pilot spool and the main spool are machined separately on CNC equipment. They are ground to a precise surface finish and matched to their corresponding bores during the sizing stage. If the fit is too loose, the pressure setting will drift. If it is too tight, the spool may stick and fail to open at the set point.

Pressure adjustment ranges
The DA series pilot operated relief valve is available with four pressure adjustment ranges: 5, 10, 20, and 31.5 MPa. The range is selected based on the maximum operating pressure of the circuit. The adjustment knob is mounted on the pilot stage and allows the operator to set the relief pressure within the selected range. Once the pressure is set, the knob can be locked in place.

Materials and surface treatment
The valve body is made from cast iron, which provides durability and resistance to deformation under repeated pressure cycles. The spools are machined from hardened steel bar stock and ground to a precise finish. The body is treated with a phosphating process to provide corrosion resistance, and all ports are sealed with protective plugs during packaging.

Manufacturing and testing
Each valve is assembled from the machined body, spools, springs, and adjustment knob. After assembly, every valve is tested on a hydraulic test bench. The valve is pressurized to 31.5 MPa to confirm that the body and seals hold pressure without leakage. The pilot stage is also tested to confirm that it opens at the correct set point. Valves that fail this test are reworked before they are packed.

Position of the valve in the circuit
In a typical hydraulic shear or bending machine, the pump runs continuously during the production cycle. It drives the main cylinder that moves the blade or the bending beam. Once the cutting or bending stroke is complete, the directional valve shifts, and the pump continues to run while the machine resets and the next workpiece is positioned. The DA series is installed in the pressure line, between the pump and the directional valve.

When the valve activates
When the machine is in the idle phase between cycles, the directional valve is centered, and the pump continues to deliver oil. Without a relief valve, the pump would push against a blocked line, and the pressure would rise rapidly. The DA series pilot operated relief valve prevents this by opening at the set pressure and diverting the excess flow back to the tank. This keeps the pressure from exceeding the limit. The valve also protects the system during sudden pressure spikes. If a blade or beam hits a jam or if the directional valve shifts too quickly, the valve opens and absorbs the spike before it can damage a hose or a seal.

How the pressure is set on this machine
The relief pressure on a shear or bending machine is set to match the maximum operating pressure of the cylinder. The technician adjusts the knob on the pilot stage while monitoring the pressure gauge on the main line. Once the gauge reads the correct pressure, the knob is locked in place. The valve holds that setting throughout the production run. If the machine is switched to a different material thickness, the pressure can be adjusted accordingly.

Why a mechanical pilot operated valve is preferred here
In this type of machine, the production run is often long, and the pressure setting remains the same for hours at a time. A mechanical valve does not require a power supply or a control signal to maintain the pressure setting. Once it is set, it stays set without drift. The DA series pilot operated relief valve provides a stable, repeatable pressure limit that requires no supervision or recalibration during the shift.

Information we need to get it right
When you send us an inquiry, we need a few details to ensure we quote the correct valve. The valve size is the first decision. The pressure adjustment range (5, 10, 20, or 31.5 MPa) is the second. The Design Number (50) identifies the current production version. If you have a circuit diagram or a photo of an existing valve, that helps us confirm the port orientation and the mounting dimensions. The more specific you are at this stage, the fewer questions we will need to ask later.

Quotation and lead time
Once we have the details, our engineering team reviews the configuration and confirms compatibility. We then provide a formal quotation with unit pricing and a confirmed lead time. For standard configurations, we typically ship within 2 to 3 weeks. For custom orders-such as a specific pressure setting or a non-standard mounting configuration-we coordinate the timeline with you during the quotation stage.

Production and testing
Your order goes into our CNC machining and assembly lines. We run each valve through a hydraulic test bench before packaging. The valve is pressurized to 31.5 MPa to confirm seal integrity. The pressure adjustment function is also verified to ensure the pilot stage opens at the correct set point.

Shipping and support
Once the valves pass testing, we seal the ports with protective caps, wrap the valve, and label it with the model number. We ship via sea freight, air freight, or international courier based on your preference. Every shipment includes an installation manual. If your project requires hydraulic schematics or 2D CAD drawings, we can provide those upon request.

Why the casting is the starting point of reliability
The DA series begins as a raw iron casting. This is not a stamped or fabricated housing. A casting allows us to machine the internal flow passages and the spool bores from a single, solid piece of metal. The wall thickness is uniform, and there are no weak points at welded joints. The valve body can withstand the repeated pressure cycles of a hydraulic system without developing cracks over time. We inspect every casting before it reaches the machining line. If we see signs of porosity or surface defects, that casting is rejected. A bad casting is not worth the machining time.

Precision machining of the pilot and main spools
The most critical components in the DA series are the pilot spool and the main spool. The pilot spool controls the pressure setting. If its fit with the bore is too loose, the pressure will drift. If it is too tight, the spool may stick and fail to open at the set point. The main spool handles the full flow of the system. Its sealing edge must be machined with a precise finish to hold pressure without leaking.

We machine both spools on our own CNC equipment. This gives us control over the fit and the surface finish. We grind the spools to tight tolerances and match each one to its corresponding bore before assembly. If a spool does not fit the bore within the specified clearance, it is set aside. We do not force a fit. The valve will leak if the fit is wrong.

Spring selection and adjustment
The spring in the pilot stage determines the opening pressure of the valve. The spring must deliver a consistent force over millions of cycles without losing its tension. We select springs from suppliers that test each batch for force consistency and fatigue resistance. During assembly, the spring is matched to the pilot spool and tested to confirm that the opening pressure is within the specified range.

Testing at 31.5 MPa
Every assembled DA valve is tested on a hydraulic test bench before it leaves the shop. We pressurize the valve to 31.5 MPa to confirm that the body and the seals hold pressure without external leakage. We also test the pressure adjustment function to confirm that the pilot stage opens at the correct set point and the main spool shifts as intended. A valve that fails this test is reworked before it is packed. This test confirms that the valve will perform as expected when it is installed on a machine.

What these steps mean for the customer

The cast iron body provides a durable housing that resists cracking under pressure cycles.

The precision-ground spools ensure consistent pressure setting and low internal leakage.

The tested spring maintains the opening pressure without drifting over time.

The 31.5 MPa bench test confirms that the valve is free of leaks before it is shipped.

FAQ

 

 

What happens if I set the relief pressure higher than the system pump can deliver?

If the relief pressure is set higher than the pump's maximum output pressure, the valve will never open. The system will not be protected from overpressure, and the pump will run against a closed circuit if the directional valve is shifted. The relief pressure should always be set below the pump's maximum output pressure.

Can the DA series be used in a system with a load-sensing pump?

Yes, the DA series can be used as a secondary safety relief valve in a load-sensing system. It provides an absolute pressure limit that protects the system in the event the load-sensing compensator fails. It should be set slightly higher than the maximum load-sensing pressure.

What is the difference between a direct-acting relief valve and a pilot operated relief valve?

A direct-acting relief valve uses a spring directly against the spool. It is simple and fast, but the pressure setting changes as the flow rate increases. A pilot operated relief valve, like the DA series, uses a small pilot stage to control a larger main spool. This allows the pressure setting to remain stable across a much wider flow range.

Can I use the DA series as a sequence valve to control multiple cylinders?

No. The DA series is a pressure relief valve. It is designed to limit pressure and divert excess flow to the tank. It does not act as a sequence valve. If you need to sequence cylinder operations, a separate sequence valve or a directional valve with a pressure-compensated flow control is required.

How does the valve behave during a rapid pressure spike?

The DA series is a pilot operated valve. During a very rapid pressure spike, there is a short delay before the pilot stage opens and shifts the main spool. During this delay, the pressure may exceed the set point briefly. The response time is fast enough for most industrial applications. If the application requires a faster response to pressure spikes, a direct-acting relief valve may be a better choice.

How does the DA series hold up in systems with frequent pressure fluctuations?

The DA series is designed for systems with frequent pressure fluctuations. The pilot operated design maintains a stable pressure setting across a wide range of flow rates. The main spool is tested for smooth movement and the spring is selected for fatigue resistance. The valve will hold the pressure setting without drifting, even in systems with constant pressure changes.

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