High Pressure Relief Valve for A4VG250 Pump

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High‑Pressure Relief Valve for A4VG250

High‑Pressure Relief Valve for Rexroth A4VG250 (Exclusive for Closed‑Circuit Systems)

Product Positioning: The A4VG250 is a variable displacement axial piston pump for closed‑circuit applications manufactured by Rexroth. Each high‑pressure port on both sides is equipped with one high‑pressure relief valve (two in total), which integrates dual functions of pressure limiting protection and charge check.

1. Core Specifications of the Valve

- Applicable Pump Model: A4VG250 (displacement: 250 cm³/r)

- Mounting Position: One valve installed at each high‑pressure port (Port A and Port B) of the pump

- Rated Pressure: 400 bar (40 MPa)

- Peak Pressure: 450 bar (45 MPa)

- Factory Setting Pressure: Standard 350 bar (field fine‑tuning available)

- Integrated Functions: Combined relief (safety valve) and charge check valve

- Material: High‑strength alloy steel spool with hardened valve seat

- Seal Material: FKM fluororubber, resistant to high pressure and high temperature

- Circuit Type: Closed‑circuit only (hydrostatic transmission)

2. Structure (Integrated 2‑in‑1 Design)

1. Main Relief Spool: Opens under overload high pressure and diverts oil to the low‑pressure side

2. Pressure‑Regulating Spring: Sets the cracking pressure (standard at 350 bar)

3. Check Valve Assembly: Opens when low‑side pressure drops to supply charge oil and prevent cavitation

4. Valve Body: Integrated with the pump housing, modular design for individual replacement

3. Working Principle (Dual Functions)

- High‑Pressure Protection (Relief Function):

When the pressure at Port A or B exceeds 350 bar, the spring compresses and the main valve opens. High‑pressure oil is discharged to the low‑pressure side, limiting the system pressure below 400 bar to protect the pump and motor from overload damage.

- Charge Function (Check Valve):

When the low‑pressure side pressure is lower than the charge pump pressure, the check valve opens. The charge pump supplements oil to prevent cavitation and provides cooling and lubrication.

4. Model & Part Identification

- Valve Part Number: R902417956 (standard relief valve for A4VG250)

- Sample Pump Model: A4VG250EP2D1/32R‑NSD10F01

- A4VG: Series code

- 250: Displacement

- EP: Electro‑proportional control

- 32R: Frame size

5. Key Features

- ✅ High‑pressure durability: Continuous operation at 400 bar and peak pressure up to 450 bar, long service life under heavy‑duty conditions

- ✅ 2‑in‑1 integration: Combines relief and charge check functions, simplifying the circuit and reducing overall costs

- ✅ Closed‑circuit dedicated: Optimized for hydrostatic travel/swing transmission with excellent anti‑cavitation and heat dissipation performance

- ✅ Individually replaceable: Modular design allows replacement without full pump disassembly, minimizing downtime

- ✅ Pressure adjustable: On‑site spring fine‑tuning to meet different working conditions

6. Typical Applications

Closed‑circuit hydrostatic transmission systems for concrete pump trucks, heavy‑duty flatbed trucks, mining machinery, asphalt pavers, road rollers and other heavy‑duty equipment.

7. Common Faults

- Low system pressure: Spool sticking, spring fatigue or check valve leakage

- Abnormal noise / vibration: Excessively high pressure setting, contaminated oil or cavitation

- Excessive heat generation: Frequent relief valve activation or insufficient charge oil supply

The A4VG250 is a swashplate-type axial piston variable displacement pump produced by Bosch Rexroth.Its high-pressure side is equipped with two relief valves, which are used to prevent overload in the hydrostatic transmission system (pump and motor), while also serving as makeup valves.Below is a detailed introduction to the high-pressure relief valves of the A4VG250:

I. Product Features

1. High-Pressure Protection: The A4VG250 has a nominal pressure rating of 400 bar and a peak pressure rating of up to 450 bar. The high-pressure relief valves open when the system pressure exceeds the set value, allowing excess oil to flow back to the tank, thereby preventing damage to the pump, motor, or other hydraulic components due to excessive pressure.

2. Makeup Function: In addition to serving as relief valves, the high-pressure relief valves of the A4VG250 also function as makeup valves. In a closed-loop system, the continuous use of hydraulic oil may lead to insufficient oil volume. In such cases, the makeup valves automatically open to replenish the system with hydraulic oil, ensuring normal operation.

3. Built-In Design: The high-pressure relief valves are typically built into the A4VG250 pump body, offering a compact structure and saving space. Additionally, the built-in design reduces external piping connections, lowering the risk of leakage.

4. Multiple Control Methods: The A4VG250 pump offers various displacement control methods, such as hydraulic control, hydraulic control with manual servo, and electrical two-point control. These control methods allow for precise adjustment of the pump's displacement according to actual needs, enabling precise control of system pressure and flow.

II. Technical Specifications (Examples of Some Models)

• Nominal Pressure: 400 bar

• Peak Pressure: 450 bar

• Displacement Range: The displacement of the A4VG250 is typically 250 cm³/rev (specific displacement may vary depending on the model and configuration).

• Control Methods: Multiple control methods are available, such as HD (hydraulic control), HW (hydraulic control with manual servo), and EZ (electrical two-point control).

III. Application Areas

The high-pressure relief valves of the A4VG250 are widely used in applications requiring high-pressure and large-flow hydraulic transmission, such as:

1. Construction Machinery: Examples include excavators, loaders, and road rollers.

2. Marine Industry: Applications include deck machinery and propulsion systems on ships.

3. Industrial Machinery: Examples include injection molding machines, presses, and machine tools.