How Valves Work

Valves are used to control the flow of water in a system.

Valves, used to control the flow of water in a system, can be mechanical, hydraulic, electric or a hybrid. In order for a valve to work, there has to be a drop in pressure between the water source and the outlet, such as a sprinkler. A drop in pressure enables the valve to close itself and an increase in pressure allows the valve to open. A problem can arise if there is a low flow of water, which does not create enough drop in pressure, so the drop in pressure has to be increased. This is accomplished by leaving the valve in question partially closed.

Valves are available in brass and plastic models with plastic models being the most popular. Both types of valves are reliable when installed in automatic systems of systems that use manual valves. However, brass valves tend to last longer in systems with manual valves. If the valves are to be installed above ground, plastic valves should have a cover to protect them from sunlight that will destroy them over time.

There are many types of valves. There are four main varieties of valves. These are isolation valves, control valves, check valves and master valves. Among these varieties of valves are automatic control valves, by-pass valves, double check valve assemblies, drain valves, flow control valves, gate valves, globe valves, master valves, normally closed valves, and pressure relief valves.

Automatic control valves are either electric or hydraulic remote control valves. These are generally located in a sprinkler system and activated by an automatic controller. These valves, often installed in an irrigation system as control valves, can also be known as section valves, zone valves or remote control valves.

Ball valves are valves that control water by using a ball that rotated through a hole in the middle of it. The water flows freely through the valve when the hole is aligned and when the ball rotates and the hole is not aligned the water flow is stopped. These valves are used generally as isolation valves.

By-pass valves are relief valves that are designed to vent excess pressure or flow.

Drain valves are automatic or manual valves that are used to drain water from an irrigation line.

Flow control valves are valves that restrict flow and consequently discharge pressure by being mechanically adjusted.

Gate valves are manual valves that have straight through flow using wedge type metal-to-metal or restricts partial seating surfaces. These valves are not for throttling section flow or for use as section valves in an irrigation system. These valves are commonly used as emergency shut-off valves which are usually installed near the water source and will shut-off the water in the whole system should an emergency arise.

Globe valves, also known as angle valves, are valves that use rubber or composition seats against the valve body to restrict or stop the flow of water. These valves can be configured as straight through or angle and are control valves that turn the sprinklers on and off. These valves are usually installed underground in a box or vault.

Master valves are automatic or manual valves that are installed at the water supply point and control the water flow into the system mainline piping.

Normally closed valves are automatic valves that do not allow water to flow unless external influences cause the valve to open. All electric valves are this type of valve.

Pressure relief valves are valves that open when the water supply pressure exceeds a preset pressure.

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