Valves

What is a valve?

The control of flow is achieved by opening, closing, or partially obstructing various passageways to achieve the correct amount of media to the next stage of the process.

Valves can be constructed in multiple connecting configurations for your pipework, to include but not restricted to, threaded, clamped, welded etc.

Each valve is designed to suit a certain application.

What is a valve made from?

A valve is a complex structure and can be manufactured from various different materials. A valve is typically made up from the following parts; Actuator, Bonnet, Stem, Plug, Seat, and the Valve Body.

These parts can be manufactured from metals (Carbon, Stainless steel, or exotic metals), thermoplastics, PTFE, PFA, PVDF,  or a combination of metals and plastics to suit the designed application.

What are the function of valves?

Valves are used for many different functions such as:

• Isolation of media, emergency fail-safe in the result of system failure, they can be failing open, or failing closed.
• Control of media, using an analogue 4-20ma or digital signal 0-10 volts from the controller, this is then directly proportional to the flow.
• Direction of media, in the means of a 3-way valve, to divert the flow from one path to another.
• One-way flow control valves, or check valves as they are commonly known, will only allow the flow of media in one direction, and prevent the back-flow of media in the other direction
• Pressure relieve valves are a safety valve to inhibit the pressure in a system from going above the safe level.

How do you size a Valve correctly?

Valve sizing is carried out using a systematic method for selecting body types, sizes, materials, pressure ratings and trim sizes based on fluid/gas, temperature, upstream/downstream pressure, flow rate characteristics, and pressure drops. Control valve flow capacity (Cv/Kv ).

The Cv-value is the numerical value of the amount of U.S. gallon water  (40-100°F) per minute, that passes the tested valve at a differential pressure  of 1,0 psi.  

The Kv-value (VDI/VDE 2173): 

The Kv-value is the numerical value of the amount of cubic meters water (5-40°C) per hour,that passes the tested valve at a differential pressure of 1,0 bar.  

This standard and the corresponding measuring standards contain equations used to predict the flow of compressible and in-compressible fluids in control valves. Slightly different forms of the basic equation are used for liquids and gases.