What is a Check Valve
or Non-return valve (NRV)?
Check valves or
non-return valves are self actuated valves and designed to prevent the reversal of flow in a piping
system. In other words we can say that Check valves are basically backflow
preventers.Valve Check continues to work even if plant loses it power,air supply or hydraulic power source. Even these flow preventers or one way valves do not need operator,s assistance to function.
How Does a Check valve Work?
Check valves are activated
by the flowing material in the pipeline.This flowing material may be gas,water ,air ,oil or steam in pipeline. The pressure of the fluid passing
through the system opens the check valve, while any reversal of flow will close
the valve.Opening of valve is basically lifting or swinging of check valve disc thus allowing the flow in one direction.Closure in check valve,
for backflow prevention, is accomplished by the weight of the check mechanism,
by back pressure, by a spring, or by a combination of these means.
Why
we use Check Valves or Non-Return Valves or one way valves?
Sometimes reverse
flow may be detrimental for equipment or process so it needs to be
uni-directional for operational safety. This operational safety is accomplished
by valve check. Valves check are self actuated and self operating devices.
- Check Valves are used to protect the equipment that can be affected by reverse flow, such as flow meters, strainers and flow control valves.
- Check Valves are used to check the pressure surges associated with hydraulic forces, for example, water hammer
- Check Valves are used to prevent the flooding that can take place if flow reversed.
- Check Valves are used to prevent the reverse flow on system shutdown.
- Check Valves are used to to prevent the flow under gravity.
- Check Valves are used for relief of vacuum conditions.
Basic Types of
Check Valves
It is very important for HVAC mechanical engineer to know about various valves being used in mechanical industry.Various check valve types have been developed to cater to the diversified requirements in piping systems in various applications.These various types of check valves offer many advantages and disadvantages .One type of check valve ideal for one application may be misfit for another application.Plant engineers have to look into many factors to decide which type of valve would be they using in that particular application.
Following are the
main check valve types used in various applications.
- Swing Check Valve
- Tilting Disk Check Valves
- Lift Check Valves
- Piston Check Valves
- Butterfly Check Valves
- Stop Check Valves
- Other Check valve types (Ball check valve, diaphragm check valve etc)
