Рет қаралды 120
PVC valves are made from polyvinyl chloride plastic. They usually have no metal parts in contact with the fluid path which makes them suitable for a variety of caustics and corrosives. PVC is also commonly used in potable water applications. In order to ensure safe drinking water, PVC valves are often certified by a third party. The typical standard for potable water is NSF 61, although other standards apply.
Like their metal counterparts, PVC valves are available in 2-way, 3-way and butterfly configurations. Common material variations include CPVC, which is chlorinated PVC. CPVC is capable of withstanding higher temperatures but cannot withstand freezing temperatures. It also costs more the PVC.
PVC valves are connected to the pipe by solvent welding or threaded end connectors. All PVC piping and valves should never be used for compressed gas applications as it can shatter into dangerous shards upon rupture.
Some features that differentiate higher quality PVC valves include a machined ball and stem after molding for lower torque and smoother operation, high quality seal materials such as PTFE and integral union nut locking devices to prevent back-off due to vibration or thermal cycling.
On/Off electric actuators open and close the valve via an electric motor. Upon receipt of a continuous signal, the motor runs until the valve is rotated 90-degree, completely closing or opening the valve. When the valve reaches the closed or open position, an internal cam on the actuator strikes a limit switch and shuts off the motor. If the electric signal is lost mid-stroke, the valve stays in mid-stroke position.
Electric actuators come in a variety of torque ratings, from as low as 15Nm to 600Nm or more. Common voltages are 24VDC and 120VAC.
Some features that differentiate higher quality electric actuators include an all-metal gear drive, a weatherproof enclosure (normally IP 67 NEMA 4X or higher), a thermostatic heater to prevent internal condensation, a manual override mechanism and a dome position indicator.
Positioning actuators throttle the valve to the desired position via an internal servo-controller. Changing the input signal (usually 4-20mA or 0- 10V) results in a corresponding and proportional change in the position of the valve. If there is a total loss of power the valve remains in the last known position. If the control signal is lost, the actuator can be programmed to fail open or fail close.
Electric positioning actuators come in a variety of torque ratings, from as low as 20Nm to 600Nm or more. Common voltages are 24VDC and 120VAC.
Some features that differentiate higher quality electric positioning actuators include a self-calibrating controller, an all-metal gear drive, a weatherproof enclosure (normally IP 67 NEMA 4X or higher), a thermostatic heater to prevent internal condensation, a manual override mechanism and a dome position indicator.
www.valworx.com/category/electric-actuated-pvc-ball-valves-on-off
www.valworx.com/category/electric-actuated-pvc-ball-valves-positioner