Water Control Valves - Plumbing resource
Water Control Valves
Published on Plumbing  |  March 25, 2010, 22:19
In Chilled and hot water systems there is a need for automatic and manual control valves to control the flow of water in piping loops. Valves such as check valves, triple-duty valves, automatic flow control valves, automatic temperature control valves, and circuit setters can maintain the flow at a specified rate, reduce pressure, regulate temperature, dampen pulses in the hydronic loops, and protect the system from serious damage by preventing instability in a hydronic systems.

Triple Duty Valves

Triple Duty Valves are three valves in one as the name implies. Triple Duty Valves act as a check valve, balancing valve, and a shut-off valve all in one valve. From the smallest hydronic loops to the largest hydronic loops triple duty valves are very a popular selection for engineers when designing hydronic loops for chilled water and hot water applications.  The triple duty valve consists of a threaded stem attached to a disc. The disc has a spring that will allow the disc to open when flow is induced throughout the loop. The disc will only allow flow in one direction and shuts whenever the flow is reverse of the normal flow. The threaded stem can be adjusted to allow a specified amount of flow through the valve and is usually set by a testing and balancing technician.  The stem can also be turned all the way down to shut off flow in the system. Those three options in one valve give the triple duty valve its name.  Triple duty valves are usually constructed of heavy duty cast iron and installed in the hydronic near the pumps.

Automatic Flow Limiting Valves

Automatic flow limiting valves are used for variable speed pumping systems where the flow of the water will vary and automatic flow valves generally include a ball type shut-off valve, pressuring measuring ports for test and balance technicians, and a strainer. The automatic flow limiting valve offers a balanced hydronic by compensating for pressure differences in the loop (provided the strainer is clean).

Automatic Temperature Control Valves

There are a number of different automatic temperature control valves from tempering valves (anti-scald) for domestic hot water use to proportional mixing or diverting valves that are used in many hot water boiler applications in commercial use.  The valves are usually adjustable or come at a set temperature for whatever the use of the valve and the need of the temperature of the water. For example, a hot water boiler with a domestic coil usually has a set point of 180°F. Of course this temperature is too hot for domestic use so a tempering valve or adjustable automatic temperature control valve is installed in the domestic hot water pipe. The valve also connects to the cold water supply usually connected at the boilers make-up water inlet. The automatic temperature control valve automatically mixes the cold water supply with 180°F water and reduces the temperature of the water to a comfortable setting so the people using this water for showers or washing dishes do not become scalded.

Check Valves

Check valves used in HVAC allow for one-way flow through a piping hydronic loop. Typically a check valve has a flapper inside the valve body that will close if flow reverses.  There are several different types of check valves and inside those types there are various differences from check valve to check valve. A swing check valve uses a disc inside it to prevent reverse flow in a hydronic loop and inside the swing check valve there are single discs and other swing check valves have two discs. A lift type check valve uses a poppet, a disc, or a ball to prevent reverse flow in a hydronic loop. Other check valve types include a foot check valve, slant disc check valve, a flap check valve, and a control disc check valve.  Whatever type of check valve you have check valves are designed to prevent reverse flow in a hydronic piping loop.

Pressure Reducing Valve or PRV

A pressure reducing valve is simply described by its name. It is a valve that reduces the pressure of the water in an HVAC hydronic loop. Typically this setting is 12 PSI but it can depend on the friction loss (head pressure) in a system so a calculation needs to be done to determine the friction loss in a hydronic piping loop.

Back Flow Preventer

A backflow preventer is a valve that is nearly like a check valve. Backflow preventers keep the water safe for domestic use and are usually installed on the make-up water pipe in hydronic loops or on the supply of any type of water used in HVAC hydronic loops.

Circuit Setters

Circuit setter valves are used to maintain a set amount of flow through a piping loop. Circuit setters are generally set by a test and balance technician who sets the valves according to the design flow of the HVAC equipment the loop is serving.


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