The purpose of a check valve is to allow a fluid to move through it in one direction, but prevent it from flowing in the reverse direction. In the case of a lift station, if we are trying to pump uphill and do not want all the water in the pipes coming back into the wet well when the pumps shut off, then a check valve should be specified immediately following the pumps.
A couple types of check valves used by Jensen Engineered Systems are swing check and ball check. A swing check uses a flapper gate with a hinge to allow uni-directional flow. One of the considerations when using a swing check is that it must be mounted in the horizontal position to properly allow the gate to open and close. If mounted in the vertical, or upside down, the gate can be forced to remain in the open position.
If site restraints require a check valve to be mounted in the vertical, a ball check valve should be used. Though a ball check can be mounted in either the vertical or horizontal and work properly, we typically reserve it for vertical applications. The design of a ball check uses a metal ball to allow uni-directional flow. When the water is flowing in the desired direction, the ball is forced out of the flow path. When the flow attempts to reverse, the ball falls back into the flow path and prevents reverse flow. When mounted in the vertical, gravity aids the ball by forcing it back into the flow path.
An isolation valve provides operation and maintenance crews the ability to manually close or open the valve to allow or prevent fluid to pass. There are numerous situations and reasons to use an isolation valve. There may be a component of the piping system that has maintenance issues. A designer could place an isolation valve on either side of the component thereby allowing maintenance crews a way to prevent flow from contacting the component.
As mentioned before, in the case of a lift station it is always recommended to have a check valve immediately following the pump. In the case that the check valve requires maintenance or replacement, an isolation valve can be placed immediately following the check to allow access to the check valve.
Some of the isolation valves which have been used by Jensen Engineered Systems include gate valves and plug valves. A gate valve uses a knife blade gate to be lowered into the flow and prevent fluid from passing. A limitation of a gate valve is that it is intended for low pressure situations. A plug valve provides the same isolation capabilities, without the pressure limitations of a gate valve.
When specifying a plug valve, it is important to consider how the operator will open and close the valve. One of the standard options is to use a 2in nut which can be opened and closed using either a T handle or a standard wrench head with handle. These options are less expensive and can be used in most applications. In the case that the fluid passing through the valve is under high pressure or flowing quickly, the operator could potentially find it physically difficult to open or shut the valve. In this case, a designer could specify a mechanical actuated valve which provide the operator with a mechanical advantage and make it physically easier to open and close. Another option is to use an electrical powered actuator that requires no physical manipulation.
Air/Vacuum Release Valves
The purpose of an air/vacuum release valve is to either let air into or out of a pressurized pipe. If a fluid in a force main has air entrapped within it, the air will tend to find high spots and collect. This can potentially hinder the flow of the fluid. An air release valve can be placed at this high spot and allow the air to exit the force main.
A vacuum release valve is necessary in a situation were a negative pressure exists in a force main. In a lift station, this could happen if the discharge point is lower that the pump intake elevation. Every time the lift station turns on, pressurizes the force main, and then turns off, a siphon will occur. Any remaining fluid in the station will be sucked through the pumps to the discharge. To prevent this, a vacuum release valve can be installed immediately following the lift station. This valve will allow air to enter the force main to break the vacuum.
An air/vacuum combination valve can be installed to provide both functions in one valve.
All air valves are specifically designed for either water or wastewater applications, so that should be a consideration.
Val-Matic® Valve & Mfg. Corp. is a leading designer, manufacturer and marketer of check valves, quarter turn shut-off valves, air valves and foot valves for water/wastewater, industrial and building markets. Valve types include Tilted Disc®, Dual Disc®, Swing-Flex®, Surgebuster® and Silent Check Valves; Plug Valves, Butterfly Valves, nine types of Air Valves, Sure Seal Foot Valves, VaultSafe family of products and the Ener-G® AWWA Rubber Seated Ball Valve