Shijiazhuang Laiye Import& Export Trading Co., Ltd. is one of the leading manufacturers and suppliers of da series — pilot operated unloading valve in China, also supports customized service. If you're going to wholesale high quality da series — pilot operated unloading valve made in China, welcome to get pricelist from our factory.
When the Pump Needs a Break
A hydraulic pump keeps running as long as the prime mover is on. It does not stop when actuators stop moving. The oil goes over the relief valve. Energy turns into heat. The pump works against pressure for no reason.
There is a better way. Unload the pump. Send the flow back to tank at low pressure. The pump still spins, but it pushes against almost nothing. The system cools down. The pump lasts longer.
That is what the DA series - pilot operated unloading valve does. It watches the system pressure. When pressure reaches the setting, the valve opens. Flow goes to tank. Pressure falls. When pressure drops below the setting, the valve closes. Pressure builds again.
Accumulator circuits use this all the time. The pump fills the accumulator. When it reaches pressure, the DA unloads the pump. The system runs on stored oil. The pump sits idle.
Presses also benefit. They hold pressure between cycles. The pump unloads instead of working against the relief valve. Less heat. Less noise. Less power.
Three sizes cover the flow range. Size 10 handles 60 L/min. Size 20 handles 120 L/min. Size 30 handles 240 L/min. Pick the size that matches your pump flow.
Pressure adjustment goes from 5 to 31.5 MPa. Set it to whatever pressure your system needs. The valve unloads when it gets there.
The DA is pilot-operated. A small pilot valve controls the main spool. The pilot valve senses system pressure and decides when to open the main valve. The result is stable unloading control.
Mounting is on a standard subplate. ISO 4401 interface. Design number is 50.
Detail Data
| Parameter | Size 10 | Size 20 | Size 30 |
|---|---|---|---|
| Size | 10 | 20 | 30 |
| Max. working pressure | 31.5 MPa | 31.5 MPa | 31.5 MPa |
| Max. flow | 60 L/min | 120 L/min | 240 L/min |
| Pressure adjustment range (MPa) | 5 - 31.5 | 5 - 31.5 | 5 - 31.5 |
| Design number | 50 | 50 | 50 |
| Brand | Onederful® Hydraulic | Onederful® Hydraulic | Onederful® Hydraulic |
| Custom | OEM / ODM | OEM / ODM | OEM / ODM |
How to Choose
Pick the size based on your pump flow. Size 10 does 60 L/min. Size 20 does 120 L/min. Size 30 does 240 L/min. Those are the maximums. Do not run right at the limit. Give yourself some headroom.
Here is an example. Your pump delivers 100 L/min. Size 20 will handle it. But you are at over 80% of capacity. Size 30 gives you more room. It runs cooler. It lasts longer. The cost difference is small. The peace of mind is not.
The pressure setting works the same on all sizes. You can adjust it anywhere from 5 to 31.5 MPa. The screw is on top. Turn it to set the unloading point.
Not sure which size fits your system? Send us your pump flow. We will look at it and recommend one. No charge. No obligation. We would rather get it right before you order than fix it after.
How to Order
We keep it simple. Send us your requirements-model, size, pressure range, quantity. Not sure about the specification? Send us your system parameters: pump flow, working pressure, circuit type. We will recommend the right valve.
We confirm availability and send you a quote with pricing, delivery time, and shipping options. For custom orders, we confirm the lead time and provide a drawing for approval.
Review the quote and confirm. We send you a proforma invoice. Payment terms: T/T for larger orders. Paypal, Western Union, or MoneyGram for smaller amounts. Payment terms are negotiable for regular customers.
For standard valves, we ship from stock within 2-3 business days. For bulk orders, 10-14 business days. Custom orders take 15-25 business days depending on complexity. Every valve goes through our 10-step inspection process before packing.
Small orders go into cartons with foam inserts. Bulk orders go into export-grade plywood cases. We ship by sea, air, railway, truck, or express-you choose. We provide tracking for every shipment.
What you get with your order
Packing list
Inspection certificate
Test report (if requested)
Installation drawing (if requested)
Custom requirements
OEM and ODM are routine. We can put your brand on the valve body and packaging. We can supply non-standard pressure ranges, special seals, or custom porting. Minimum for custom orders is 10 pieces. Send us your drawing and requirements-we will review and confirm.
Where You See These Valves
Accumulator circuits. This is the most common application. The pump charges the accumulator. When pressure reaches the set point, the DA unloads the pump. The accumulator supplies flow for the next cycle. The pump sits idle between charges. Less wear. Less heat.
Presses. A press holds pressure during the forming cycle. The pump does not need to run against the relief valve the whole time. The DA unloads the pump between cycles. Oil stays cooler. The pump lasts longer.
Clamping systems. A fixture clamps a workpiece. The clamp holds pressure. The pump unloads while the clamp stays engaged. No need to keep the pump working against pressure.
Test stands. Hydraulic test circuits often have idle periods between tests. The DA unloads the pump during those idle periods. Saves power. Reduces heat build-up.
Mobile equipment. Some mobile machines have auxiliary functions that cycle on and off. The DA unloads the pump when the function is not active.
Hydraulic power units. Multiple circuits share one pump. The DA unloads the pump when no circuit requires flow. The pump only works when it needs to.
About the Company
We started in 1988. That is more than 35 years of dedicated focus on pressure valve component manufacturing. Our team has over 200 people-not just production staff, but engineers, quality control specialists, and sales professionals who understand the product from the inside out. Some have been with us for twenty years. They know the process.
We are a manufacturer, not a trading desk. We belong to Hebei Wendefu Hydraulic Technology Co., Ltd., a high-tech enterprise that focuses on R&D, production, and sales of hydraulic valves, directional valves, pressure valves, flow valves, accessories, and special components. Machining, assembly, and testing all happen in our own facility. Everything under one roof. This gives us control over quality and delivery.
We ship over 10,000 containers a year. Customers in more than 20 countries-Russia, Europe, the Middle East, South America, Southeast Asia. Our valves go on agricultural equipment in Poland, construction machines in Chile, press builders in Thailand, and mining gear in South Africa.
Our approach to quality
We do not rely on spot checks. At least 10 inspection procedures are carried out before each batch is shipped. Each valve is tested on dedicated test stands for pressure settings, leakage checks, and functional performance. Every valve comes with a batch record that tracks the test data. If you request a test report, we include it with the shipment. This is our commitment to reliable operation-because we know you need more than just parts; you need peace of mind.
R&D and engineering
We have strong technical strength and processing capacity. We have hired a group of senior industry experts as senior consultants. Our engineering team continuously optimizes product performance and quality, introducing new technologies to make mechanical work simpler and more efficient. We do custom work-OEM and ODM are routine. If you have a drawing, we can build to it. Minimum for custom orders is 10 pieces. For standard valves, there is no minimum.
What we offer
12-month warranty from Bill of Lading date. Technical support from people who understand hydraulics. Shipping by sea, air, railway, truck, or express-with multiple transportation options near the port for fast delivery. Packaging in cartons for small orders and plywood cases for bulk orders. Our sales managers provide professional analysis and solutions tailored to your application.
If you need a reference in your industry, ask. We can share case summaries. If you want to see the shop, we can arrange a video call. Visitors are welcome too, with advance notice.
FAQ
Q: What if the valve chatters during unloading?
A: Check for air in the system. Check if the flow is within the valve's rating. Check the oil temperature. Chattering may also indicate a loose adjustment screw or worn pilot valve.
Q: Can the pilot section be replaced separately?
A: Yes. The pilot valve is a replaceable cartridge. If the pilot stage fails, you can replace it without removing the main valve body from the subplate.
Q: What does an unloading valve do?
A: It sends pump flow back to tank when system pressure reaches a set point. The pump runs at low pressure. It saves energy, reduces heat, and extends pump life. The DA does this automatically.
Q: Does the DA have a solenoid?
A: No. The DA is pilot-operated by system pressure. No electrical connection is required.
Q: Can the DA replace a relief valve?
A: No. They do different jobs. The DA unloads the pump at a set pressure. A relief valve protects the system from overpressure. You need both in many systems.
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