There are some essential factors to consider when selecting an instrument valve. Some of the essential criteria for valve selection are listed below. Each application will give higher priority to:
Basic valve/package design
Pressure fluctuation
Pressure and temperature considerations
Other key factors include fluid media, specifications and standards, actuator design options, flow analysis, and orifice size.
It is critical that all aspects of the system are evaluated to determine the appropriate design before valve specifications are developed. Understanding the various operating conditions will greatly influence the final design choice.
Design of main instrument valve
Understanding the various design methods for meter valve packing and available valve design types plays an important role in the specification process. In its basic core, the valve includes a control assembly, such as a ball or needle, and sometimes an automatic drive for valve operation rather than manual operation. The meter valve seat controls the flow of material, while packing limits leakage between the seat and the drive element. Structural material, stiffness, stem position, and correct valve selection greatly affect the overall performance of the valve. In general, of all valve designs on the market, the following four valve types will be used for flow control, analysis, testing, and instrumentation applications to ensure maximum safety.
Ball valve
A ball valve consists of a spherical component used to stop or start the flow of fluid. Operationally, when the valve handle is rotated to the open position, the ball is rotated to move through the hole of the ball in the direction of the valve inlet and outlet. When the valve is closed, the ball rotates so that the hole closes the flow opening of the valve body and the flow stops. Most ball valve actuators are quick acting and require only a quarter turn of the valve handle to open and close the valve.
The most popular instrument ball valves have a rated pressure of up to 3,000 PSI, a temperature of up to 350 ° F (176 ° C) , and a PFA (perfluoroalkoxy polymer) seat to provide single (on-line) , two-way angular mode and three-way connection. High-quality ball valves have a pneumatic test seat at 1,000 PSI pressure with zero nitrogen leakage. The bodies of these ball valves shall be hydrostatically tested at 3000 psi and the seats shall be hydrostatically tested at 2000 psi.
The popular ball valve design is available in 316 stainless steel and brass, and combines integral packaging with clean and accurate samples, as well as a design that allows insertion for easy-to-replace packaging.
Double block and exhaust valve
The JPGA double blocking relief valve or DBBV replaces three stand-alone valves, two isolation valves and one relief valve. Dual blocking and exhaust valves are isolated from upstream and downstream processes and pressures.
A dual isolation and exhaust valve prevents process fluid from entering the area being operated. When the phlebotomizer is opened, both pipe valves are closed. If fluid leaks through the first valve, the drain will drain before pressurizing the chamber between the upstream and downstream valves. If the bleeder (which may be a needle valve) is blocked, the downstream valve will block the flow of process fluid.
Needle valve
Needle valves use precision-designed tapered pins to gradually open space for fine flow control. Flow can be controlled and adjusted by the use of a needle. The needle valve has a relatively small hole with a long tapered seat and a needle plunger at the end of the screw that precisely matches the seat to close the valve.
The plunger contracts as the needle valve screw rotate, allowing fluid to flow between the seat and the plunger. However, when the plunger is fully retracted, the precise adjustment of the flow can be controlled. Needle valves are commonly used in vacuum systems where accurate control of gas flow is required at low pressure. They are often used as part of other more complex valve systems.
Meter needle valves are available with a screw or integral bonnet. Most have a rated pressure of up to 6000 PSI, a temperature of up to 4500 °F (2320 °C) , and have straight and angled channels.
Check valve
A check valve (also known as a one-way valve) is a valve that generally allows a medium (liquid or gas) to flow in only one direction.
Check valves include two-port valves, which means they have two openings in the body, one for fluid or gas entry and one for media exit.
