Type A and DIF Type Straight-Through Check Valve

I. Product Introduction

The check valve (English name: Check Valve), also known as a non-return valve, is a fundamental pipeline protection control valve. Its core function is to block reverse flow of media, prevent hydraulic system oil from flowing back, and stop reverse flow of compressed air in pneumatic systems. It ensures unidirectional and orderly flow of media in hydraulic and pneumatic pipelines, stabilizing circuit operating pressure. Check valves are classified into two main categories: standard check valves and pilot-operated check valves, suitable for all operating conditions in hydraulic energy storage and pneumatic automatic control pipeline systems.

II. Types and Connection Methods

1. Standard Check Valve

Available in two structural types:

(1) Straight-Through Check Valve: Uses screw-type pipeline connection, convenient for disassembly and assembly, suitable for embedded installation in straight pipelines.

(2) Right-Angle Check Valve: Adaptable to three connection methods: threaded, plate-mounted, and flanged connections, suitable for multi-condition pipeline layout selection.

2. Pilot-Operated Check Valve

Also known as a shut-off valve or pressure-retaining valve, its basic function is equivalent to a standard check valve, normally blocking reverse oil flow. The difference is that it can rely on external control hydraulic force to forcibly open the valve core, breaking the unidirectional flow restriction and enabling bidirectional oil flow. It is widely used in oil circuit locking and pressure-stabilizing applications.

III. Structure and Leakage Types

Pilot-operated check valves feature a standard tapered valve core structure with excellent sealing performance, effective oil circuit closure and locking, and stable pressure-retaining performance. Based on control oil pressure relief methods, they are classified into two types:

1. Internal Leakage Type: Suitable for hydraulic oil circuits without back pressure at the oil outlet. The pressure relief structure is built-in for a compact design.

2. External Leakage Type: Suitable for complex oil circuits with back pressure at the outlet. Features an external pressure relief channel for controllable oil circuit pressure regulation, adaptable to high-pressure circuits.

IV. Working Principle

1. Standard Check Valve: When media flows forward, the media thrust opens the valve core to conduct the oil circuit; when media bears reverse pressure, the media pressure presses the valve core against the sealing surface, closing and blocking reverse flow, achieving unidirectional self-locking flow throughout.

2. Pilot-Operated Check Valve: Without control oil pressure input, it functions as a standard check valve, allowing one-way oil flow and reverse shut-off locking. When control pressure oil is connected, hydraulic thrust drives the internal push rod to open the tapered valve core, enabling bidirectional oil circuit conduction for on-demand reverse oil discharge, pressure relief, and direction change. When control oil pressure is removed, the valve core automatically resets and closes, re-locking the oil circuit for pressure retention.

V. Core Product Features

1. Reverse Flow Protection: Prevents reverse flow of oil, gas, and hydraulic media, protecting front-end equipment such as oil pumps, pneumatic components, and accumulators.

2. Tapered Valve Core Sealing: High precision fit, extremely low leakage after closure, maintaining oil circuit pressure over extended periods with excellent pressure-retaining performance.

3. Comprehensive Type Selection: Straight-through and right-angle structures available, with multiple connection methods adaptable to on-site pipeline installation.

4. Bidirectional Operation Adaptability: Standard type for one-way shut-off, pilot-operated type for controllable bidirectional flow, integrating shut-off, pressure retention, and pressure relief functions.

5. Professional Pressure Relief Classification: Internal and external leakage types for circuits with or without back pressure, adaptable to all high and low-pressure hydraulic conditions.

6. Wide Media Compatibility: Suitable for hydraulic oil, emulsion, compressed air, and other media, universally applicable in hydraulic and pneumatic systems.

VI. Application Fields

Widely used in hydraulic pump stations, pneumatic automatic control systems, construction machinery hydraulic circuits, accumulator energy storage oil circuits, machine tool hydraulic equipment, and pneumatic valve pipelines. Used for media anti-backflow, oil circuit lock and pressure retention, and circuit pressure stabilization protection, preventing equipment pressure loss and component reverse operation failures caused by media backflow.

VII. Usage Precautions

1. Strictly verify media flow direction during installation, and follow valve body flow direction markings to avoid reverse installation that would lose shut-off function.

2. For high-pressure circuits with back pressure, prioritize external leakage type pilot-operated check valves; for circuits without back pressure, use internal leakage type.

3. The control oil pressure of pilot-operated check valves must match the system rated pressure; insufficient control pressure will cause incomplete valve core opening.

4. Regularly inspect tapered valve core sealing surfaces during pressure-retaining operations; impurity wear can cause internal oil circuit leakage and failure to lock pressure.

5. Select threaded, flanged, or plate-mounted connection types based on pipeline disassembly frequency to improve maintenance convenience.

6. For long-term idle oil circuits, drain residual media from the valve chamber to prevent impurity corrosion of the valve core, which may affect opening/closing sealing performance.