INDUSTRIAL VALVES

Valve

A mechanical device that is used in industrial piping to control the flow of fluids.


The valves used for chemical processing plants can be divided into two broad classes, depending on their primary function:

Shut-off valves (block valves) → to close off the flow.

Control valves → to regulate flow

A valve selected for this purpose should give a positive seal in the closed position and minimum resistance to flow when open.

Valve commonly used for this purpose: Gate, plug and ball valves

A valve selected for this purpose should be capable of giving smooth control over the full range of flow, from fully open to closed.

Valve commonly used for this purpose: Globe valve & Butterfly valve (often used for gas and vapour)

TYPES OF VALVES

GATE VALVES

This type of valve is used where flow rate are not restricted and should not used to throttle flow for extended periods

Gate valve materials and their application:

Positions:

Maintenance

Widely used in the industry and is good choice for on-off service and infrequent operation

Closed: Gate is placed across the pipe’s opening.

Open: Gate is raised completely out of the flow line.

Cast iron gate valve – water, lubricant & low pressure steam services

Alloy gate valve – high temperature & high pressure services

Stainless steel gate valve – corrosive, high temperature & low temperature services

Use lubricant to moving parts

When closing a gate valve, operator should take care not to damage valve seats

BALL VALVES

A ball valve is similar in design and operation to a plug valve. The flow control element, however, is in the shape of a ball.

Shouldn’t be used for throttling services

Ball valves are not designed for excessive temperature because the seats are made of plastic-coated material that tends to breakdown under high temperature

The ball has an opening or port which allows fluids to pass through.

Ball valves are quick opening.

PLUG VALVES

Plug is made out of a solid piece that has as opening through it.

The valve is positioned by turning a lever

Quick opening (one-quarter turn), very popular in the process industry

Commonly design for fuel gas piping systems, low pressure situations, slurry and lubrication services, on/off services, low temperature services and multi-port operation

Maintenance

Should never used in throttling

Most plug valve should be limited to temperature under 480°F.

GLOBE VALVES

In a globe valve, the flow path changes in direction compared to gate valve that the flow through is in a straight line.

This globe valve is preferred to use for services that require frequent valve operation.

Globe valve materials and their application:

Cast iron globe valve – water, lubricant & low pressure steam services

Bronze globe valve – low temperature & low pressure services

Stainless steel globe valve – corrosive, high temperature & low temperature services

BUTTERFLY VALVES

Physically is smaller than the other valves

Designed to be operated at low temperature and low pressure.

Commonly used for throttling and on/off services

Commonly found in cooling water and heat exchanger system

CHECK VALVES

Check Valve is designed to prevent reverse flow and to avoid possible contamination or damage to equipment

It limits backflow but not considered tight shutoff

Check Valve Design

Swing Check Valve

Lift Check Valve

Ball Check Valve

Check valve materials and their application:

Bronze check valve – low temperature & low pressure services

Brass check valve – low temperature & low pressure services

Alloy check valve – high temperature & high pressure services

DIAPHRAGM VALVES

This valve does not have a plug or disc. Instead, it uses a flexible diaphragm to control flow.

Diaphragm Valve Design

Diaphragm valve is the best valve for handling sticky or corrosive fluids or other substances that require high purity.

Weir Diaphragm Valve

Nonweir Diaphragm Valve / Straight-through-diaphragm Valve