The principal advantages of this type of valve include the clear and unobstructed waterway offered when the valve is opened, the absence of soft packing to wear out, its suitability for hot water, and the fact that it can be completely and quickly opened by a one-quarter turn of the handle.
There are two principal objections to the valve: one arises from the possible water hammer which may result from the too quick manipulation of the valve; and the other is that when the key becomes badly worn the valve may leak or jam and it is difficult to make repairs. Such valves are used almost exclusively as corporation or curb cocks and are quite popular on faucets for kitchen sinks.
Check valves are used to prevent a backward or reverse flow through a pipe line. They may be installed on the discharge end of a pump to prevent back flow through the pump when it is stopped, or a back-water valve may be installed on a house drain or house sewer to prevent the back flow of sewage into a building, or in many other situations.
In operation a back-water valve for a drainage pipe, the reversal of flow through the valve will force the closing disc into place thus cutting off the flow. In the installation of the check valve care should be taken that it is placed in the correct position and that a valve designed for a horizontal pipe is not placed on a vertical pipe or a vertical valve is not placed on a horizontal pipe, etc. Check valves are available for all positions.
A balanced valve, is used on pipe lines operating under such a high pressure that the opening of a gate valve or the closing of a globe valve against the pressure would be difficult. Balanced valves are also used on automatic-control devices such as filter rate controllers, engine governors, water-closet tanks, pressure regulators, etc. The valve has an inlet and an outlet end and it must always be placed with its inlet up stream. The pressure is then exerted equally against both discs and to move the discs it is necessary to overcome only the friction of the valve parts and to move the weight of the mechanism.
Pressure regulators may be used on water-supply lines where the supply pressure is greater than that desired in the plumbing system. They should be used in all cases where the pressure may exceed 80 to 90 lb. per square inch for long periods of time. Such a condition often arises in tall buildings and occasionally in hilly cities. Pressure regulators can be made to give any difference of pressure desired but the regulators available on the market are commonly limited to a minimum of 14 lb. per square inch for a pressure of 40 lb. Per square inch and a minimum of 40 lb. per square inch for a pressure of 200 lb. per square inch. Between these limits almost any desired pressure can be obtained.
The desired low pressure is fixed by turning the nut, thus opening or closing the balanced valve which is supported on the flexible disc and the spring. In operation, if the pressure below the valve tends to increase beyond the fixed amount the pressure in the chamber is increased forcing the disc up and partially closing the valve, thus reducing the pressure below the valve. If the pressure below the regulator becomes too low the pressure on the flexible disc is relieved and the spring opens the balanced valve in the regulator.
Another type of regulator is a less expensive type than the one described above but it is suitable only for the smaller sizes of pipe. It operates as follows: The high pressure from the inlet side operates against the disc (the lower disc) to hold the valve open. The low pressure on the outlet side of the valve operates against the disc (the upper disc) which is larger in area than the other disc. The two pressures, with the aid of the spring, just balance each other to hold the valve open in the correct position. Desired differences in pressure are obtained by adjusting the spring by turning the screw.
Wherever pressure-reducing valves are installed on the service pipe of a building a by-pass should be provided for use when the valve is out of order. A pressure-relief valve should also be used to prevent the generation of excessive pressures in the plumbing system.
Pressure-relief or safety valves
Pressure-relief or safety valves are used to prevent dangerously high pressures in plumbing systems, and for many other purposes. They are essential on hot-water supply systems where check valves are used to prevent the back flow of hot water and provision is not made for the expansion of the water or the possible generation of steam. The disc is held in place by an adjustable connection in the spring. When the pressure becomes too high, the disc is forced off its seat and the pressure in the tank or conduit is relieved. The valve should be designed with a free opening equal to or greater than the cross-sectional area of the pipe in which the pressure is to be relieved.
An air-relief valve are used on water-supply systems in which air may become entrained to such an extent as to become a nuisance. If used, the water-supply pipes should be laid out on such a slope that air will rise through the pipes to the valve which is placed at the highest point on the system. The valve operates as follows: When the valve is filled with water the float presses the valve shut and no more water can escape. A bubble of air, rising through the air-relief pipe, will enter the valve chamber and displace some of the water therein. The float will drop thus opening the valve to release the air. Water will immediately follow into the valve chamber raising the float and closing the valve again.
Float-controlled valves are in very common use in automatic apparatus used in plumbing installations. They are used principally on flush tanks, storage tanks, and in all places where it is desired to maintain a constant level of water in a reservoir. A common type of float-controlled valve used in a water-closet flush tank. Many other types and modifications are used, as there is not a complete plumbing installation in any building that does not contain a float-controlled valve.
Common pump valves
The most common type of valve used in the suction and discharge chambers of pumps acts as a check valve allowing the water to flow in one direction only. Pressure beneath the valve lifts the leather disc off of the valve seat uncovering the port and permitting the passage of water. On the release of the pressure beneath the valve the reverse tendency of the water, aided by the valve spring, forces the disc back on to the seat. A foot valve consists of a large number of small “common” valves placed in the bottom of the foot piece. Another type of foot valve consists of a single, hinged flap in the place of the many small valves.
A butterfly valve consists of a disc, somewhat like the damper in a stovepipe, which is shaped to fit the inside of the pipe as far as the disc will turn. When the valve is closed the disc fits against a ground faced seat, but unfortunately it is difficult to make and to maintain a tight fit for such a valve. Butterfly valves are used in automatic apparatus, in throttle valves, and as quick-closing valves.
Needle valves are used in the handling of gases or where it is desired to obtain a very fine adjustment of the opening of the port.
Four-way and three-way valves
Four way and three-way valves are used in special mechanisms where it is desired to divert the flow from one incoming channel to any one of two or three possible outlet channels, or where it is desired to connect an incoming and an outgoing channel immediately after a different pair of incoming and outgoing channels have been disconnected.
The pet cock, air cock, or faucet, is used as a drain for pipe lines, valves or appurtenances; to test containers for the presence of liquid or gas under pressure behind the pet cock; for connecting pressure gages; and for other useful purposes. They are seldom threaded for pipe larger than /3/8 in.
The stop-and-waste valve, is used on water-supply lines, and so operates that when the water supply is shut off the water remaining in the pipe, on the non-pressure side of the valve, will drain out through the waste which is opened when the pressure side of the valve is shut off. A stop-and-waste valve should be installed on the house end of all service pipes where the service pipe comes through the basement wall of the building, or if a meter is installed it should be placed close to the meter and on the street side thereof. This type of valve is essential to the protection of the water pipes against freezing when the heat and water are turned off in a building in cold weather.
Water-closet flush valves
Water closets may be flushed by admitting water directly to the bowl of the closet from the water-supply pipes of the plumbing system. In order to avoid the use of an excessive amount of water a valve should be used which will remain open just long enough to deliver the required amount of water and will then close automatically. It should be so designed that it cannot be held open for full flush.
Many types of water-closet flush valves are manufactured, each showing some difference from the others.