The Necessary Precautions for Using Gate Valves

Taking the necessary precautions for using gate valves provides powerful control over the opening/closing of critical piping systems across countless industrial applications. However, their unique operating characteristics require some basic precautions to ensure safe and reliable performance throughout the valve’s service life.

Failure to follow the proper procedures can lead to serious leaks, unintended valve motion, or catastrophic failures with dire consequences.

The Necessary Precautions for Using a Gate Valve:

• Hand wheels handles and transfer mechanisms must not be used for lifting, and collisions are strictly prohibited.
• The double-disc gate valve must be installed vertically (i.e., the valve stem in the vertical position and the hand wheel on top).
• The gate valve must be opened before opening the globe valve (to balance the pressure difference between the inlet and outlet and reduce the opening force).
• According to the product instruction manual, the gate valve is installed with a transfer mechanism.
• If the valve is used and closed frequently, it must be lubricated at least once a month.
• Gate valves are only to be used for fully open and fully closed operation on various pipelines or equipment, and are not allowed to be used for throttling.
• For gate valves with hand wheels or handles, do not add auxiliary lifts during operation (if the seal is not tight, inspect and repair the sealing surface or other parts). The hand wheel and handle are rotated clockwise to close, and counterclockwise to open. The gate valve equipped with a transfer mechanism should be used according to the product instruction manual.

Installation requirements:

• The location and height of installation, as well as the entry and exit directions, must comply with the design requirements. The connections must be secure and tight.
• The handwheels of different manual valves installed on the insulated pipes must not be facing downward.
• Appearance inspection must be performed before valve installation. The valve nameplate must comply with the current national standard “General Valve Markings” for valves with an operating pressure exceeding 1.0 MPa that function as main line shutoff valves. Rigorous strength and performance tests must be conducted before installation, and they can only be used after passing the test.
• During the strength test, the test pressure is 1.5 times the rated pressure and the duration is not less than 5 minutes. The valve shell and packing must be free of leakage to be qualified. During the tightness test, the test pressure is 1.1 times the rated pressure; the test pressure must comply with the requirements of GB 50243 standard throughout the test duration, and the sealing surface of the valve disc is qualified if there is no leakage.
• The use of handwheels, handles, and transfer mechanisms for lifting is not allowed, and collision is strictly prohibited.

Potential risks of improper gate valve use:

Although gate valves excel in strong isolation, there are some inherent risk factors that need to be paid attention to:

Trapped pressure:

The gate valve design has a cavity between the gate and the valve body where fluid can be trapped. This can lead to dangerous pressure buildup if not properly vented before maintenance.

Valve binding:

Over time, debris, scale, or burnt solids can cause the gate to stick or seize within the valve body, restricting operation. This can prevent tight shut-off and lead to leakage.

Valve stem explosion:

The rising stem design of gate valves means that the closing forces act directly on the stem. Failure to relieve these forces can allow the gate and stem to explode when disassembled.

Installation issues:

Improper alignment or uneven loading of the gasket during installation can cause rapid deterioration of the seating surfaces, leading to fugitive emissions and leaks.

You can learn more about common issues with gate valve use from our previous article.

Proper Installation and Operation of Gate Valves

How should the maintenance of flanged gate valves be carried out? Following some direct installation and operating practices can help mitigate these potential risks with flanged gate valves:

Installation Alignment

Gate valves should be installed such that the centerlines of the inlet/outlet and the valve cavity are in optimal alignment. Use precision gaskets or ground-in gaskets to avoid ready-made/skewed positions.

Gasket Selection

Always use full-face peripheral gaskets sized to the raised face dimensions as per code requirements. Spiral wound gaskets may be needed for high-temperature applications.

Torque Procedures

Follow the torque sequence and values specified by the manufacturer – do not over or under-tighten the flange bolts. Periodically re-check to maintain proper compression.

Pressure Termination

Never attempt to disassemble a flanged gate valve with trapped pressure in the body cavity. Always provide a venting system with drain ports at the top and bottom.

Lubrication

Regularly lubricate the gate valve stems and body seats to prevent sticking or galling. Proper lubricant material prevents damage and increases cycle life.

Cycle Testing

Partially opening and then re-closing the gate valve can cause the gate to become stuck and should be avoided. Operate only in the fully open or fully closed position.

Gate Protection

Keep the gate in the open position when not in service. Closed gates can cause damage from continuous flow impact.

Conclusion

Ultimately, obtaining flanged gate valves from an established manufacturer adhering to global standards provides the foundation for safe and reliable performance. Appropriate materials, engineering designs, and pressure/temperature ratings suited for your application are essential.