Water Valves Information
Water valves are designed to handle and control hot water, cold water, ground water, potable water, salt water and/or wastewater. Valves are a part of many daily-used machines and can perform a variety of functions. The three common valve functions include stopping and starting flow, throttling (control) flow, and acting as a non-return check for flow (check).
Stop/Start valves are used for systems that do not need the flow throttled. The valve opens to allow the flow and closes to stop flow.
Throttle or control valves control the speed and capacity of flow through the system.
Non-return or check valves control the direction of flow. Flow in the desired direction opens the valve, while flow in the oppose direction forces the valve closed. These valves are important for preventing backflow to systems in applications such as wastewater management.
Method of Control
The mechanism to control flow can vary based on the application of the valve. In general, there are two means of controlling flow through a valve.
Linear motion valves use a closure member that moves in a straight line to allow, stop or throttle the flow. The closure device could be a disc, slat, or flexible material like a diaphragm. The closure device can be used to:
- Move a disc or plug into or against an orifice
- Slide a slat, cylindrical, or spherical surface across an orifice
- Move a flexible material into the flow passage
Rotary motion valves rotate a disc or ellipse about an angular or circular shaft extending across the diameter of an orifice.
Quarter turn valves will be in their fully open or fully closed state after a 90° turn of the stem.
There are many types of water valves.
- Ball valves provide tight shut-offs, but are not suitable for sanitary applications.
- Butterfly valves permit flow in only one direction.
- Check valves are self-actuating and prevent the reversal of process flow.
- Diaphragm valves separate the flow of water from the closure element.
- Directional valves steer flow through selected passages.
- Diverter valves redirect process flow.
- Drain valves reduce surplus media.
- Float valves open or close automatically as the level of a fluid changes.
- Foot valves are check valves with a built-in strainer.
- Gate or knife valves are linear motion valves in which a closure element slides into the flow to shut off the stream.
- Globe and pinch valves are other types of linear motion devices.
- Needle valves have a slender, tapered point at the end of a valve stem.
- Poppet valves open and close ports with a sealing device and spring.
- Plug or stop-cock valves are designed for both on/off and throttling functions.
Other types of water valves include sanitary or hygienic valves, sampling or dispensing valves, shut off valves, solenoid valves, and toggle valves.
There are many types of valves which can be used for water applications. Each valve type has a unique construction to ensure proper operation in its specific application. For a more extensive description on the components of a valve please see the selection guide for Industrial Valves. Basic components are listed below.
Basic parts of a valve.
- The body of the valve holds the parts together.
- The bonnet is the cover for the opening in the body. The bonnet can also support internal valve parts, such as the stem, disk, and actuator.
- Trim is a term used for the replaceable internal parts such as the disk, seat, stem, and sleeves used to guide the stem. The trim is responsible for the basic motions and flow control features of the valve.
- The disk and seat provide the capability for permitting and prohibiting fluid flow. The system is under full pressure when the disk is closed. The seat provides a surface for the disk to seal to in order to stop the flow.
- The stem is responsible for the movement of the disk, plug or the ball for opening or closing the valve. It is usually forged and connected to the valve hand-wheel, actuator, or the lever by threading. The stem moves the disc in a linear or rotary movement to open or close the valve.
- Stem packing is used to form a tight seal between the stem and the bonnet. The packing is fitted with one of several components: a gland follower, a gland, stuffing box, packing material, or a backseat. Packing is important in preventing damage to the stem and fluid or gas loss.
The yoke and yoke nut are used to connect the body with the actuating mechanism. The yoke must be strong enough to withstand the forces, movements, and torque developed by the actuator. The nut is used to control the movement of the stem.
Water Valve Actuation
The valve actuator operates the stem and disk to open and close the valve. There are several types of actuators depending on the needs of the system such as the torque necessary to operate the valve, speed, and the need for automatic actuation. Some water valves are actuated manually, by a hand wheel or crank, or with mechanical devices such floats and cams. Others are actuated by electric, pneumatic, electro-hydraulic, or hydraulic methods.
Manual/hand operated actuators use a hand-wheel or crank to open or close the valve. They are not automatic but offer the user the ability to position the valve as needed. Manual actuators are used in remote systems that may not have access to power, however they are not practical for applications that involve large valves. The hand-wheel can be fixed to a stem or hammer which allows for the valve to be pounded open or closed if necessary. Gear heads can be added for additional mechanical advantage and open/close speed.
Electric motor actuators permit manual, semi-automatic, and automatic operation of the valve. The motor is usually reversible and used for open and close functions. The high speed motor is connected through a gear train to reduce the motor speed and thereby increase the torque. The actuator is operated either by the position of the valve or by the torque of the motor. A limit switch can be included to automatically stop the motor at fully open and fully closed.
Solenoid operated valves use hydraulic fluid for automatic control of valve opening or closing. Manual valves can also be used for controlling the hydraulic fluid; thus providing semi-automatic operation. A solenoid is a designed electromagnet. When an electric current is applied, a magnetic field is generated around the wire. An iron "T" or plunger is put in the center of the coil to concentrate the magnetism. Since iron is a strong magnetic conductor and air is not, the "T" is drawn by the magnetic field into a position where the magnetism can travel 100% through the metal conductor. The moveable "T" acts as the actuator of the valve. Solenoid valves can be arranged such that power to the solenoid either opens or closes the valve. One application of solenoid valves is to supply the air to systems like pneumatic valve actuators. These valves are not practical for large systems because their size and power requirements would be excessive.
Pneumatic operated valves can be automatic or semi-automatic. They function by translating an air signal into valve stem motion by air pressure acting on a diaphragm or piston connected to the stem. Pneumatic actuators are fast-acting for use in throttle valves and for open-close positioning.
Hydraulic actuators provide for semi-automatic or automatic positioning of the valve. They are used when a large force is required to open the valve, such as a main steam valve. With no fluid pressure, the spring force holds the valve in the closed position. Fluid enters the chamber, changing the pressure. When the force is greater than the spring force, the piston moves upward and valve opens. To close the valve, hydraulic fluid (such as water or oil) is fed to either side of the piston while the other side is drained or bled.
Self-actuated valves use the system fluid to position the valve. These are commonly found in relief valves, safety valves, check valves, and steam traps. Because these actuators use the fluid in the system, no external power is required.
There are many connection types for water valves. Examples include compression fittings, bolt flanges, clamp flanges, union connections, tube fittings, butt welds, and socket welds. Water valves with internal or external threads for inlet or outlet connections are also available.
The material of the body and disk in the water valve are very important when selecting a valve for your application. An important consideration is whether or not the body will be exposed to the media. The temperature and corrosiveness of the media can affect to wear of the material in the valve. Water valves are generally made from metal or plastic.
Metal water valves are made of:
Plastic water valves are made of:
- Acetal polymers offer excellent lubricity, fatigue resistance, and chemical resistance.
- Polyvinyl chloride (PVC) provides good flexibility, smooth surfaces, and nontoxic qualities.
- Chlorinated PVC (CPVC) is suitable for high temperature applications and is used in hot water distribution.
- Polytetrafluoroethylene (PTFE) exhibits a high degree of chemical resistance and a low coefficient of friction.
- Polyethylene (PE) is a soft, flexible and tough plastic with outstanding electrical properties but poor temperature resistance. It is prone to stress cracking and has poor resistance to ultraviolet (UV) light.
- Polypropylene (PP) is similar to PVC, but can be used in exposed applications because of its resistance to UV, weathering and ozone.
Polyvinylidene fluoride (PVDF) has good wear resistance and excellent chemical resistance, but does not perform well at elevated temperatures.
Performance specifications include valve size, pressure rating, number of ports or ways, media temperature, and valve flow coefficient. For more detailed information on the performance specifications of valves, please see the selection guide for Industrial Valves.
AWWA certified valves meet the requirements of the American Water Works Association (AWWA).
Armstrong | Dwyer | RoyMech
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