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