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What are Diaphragm Valves?

Diaphragm valves acquire their name from the flexible disk that comes in contact with a seat at the top of the valve body to form a seal. Diaphragms are typically recognized for being flexible, pressure responsive elements that transmit force to control a valve. They are related to pinch valves, but utilize an elastomeric diaphragm instead of an elastomeric liner in the valve body to separate the direction of flow from the closure element.

How Diaphragm Valves Work

As diaphragm valves are linear motion valves, they are often used to start, stop, and control fluid flow. In terms of design, the flexible diaphragm is connected to a compressor by a stud that is molded into the diaphragm. With manual diaphragm valves, control is acquired by a variable and precise opening that controls pressure drops. A handwheel can be turned until the desired amount of media is flowing through the system. For start and stop applications, the handwheel is turned until the compressor pushes the diaphragm against the bottom of the valve body to stop flow or lifts from the bottom until flow is able to pass through.

Weir-type diaphragm valves, on the other hand, are better at throttling than straight-through variations since the design’s large shutoff area along the seat provides it with characteristics of a quick-opening valve. In this configuration, the diaphragm acts as the gasket of the valve to seal against leaks between the body and bonnet cap. Now that we have briefly introduced the most common types, those of which are Weir-type and straight-through diaphragm valves, we will cover the most common actuating mechanism used to power systems with such valves.

Valve Actuators

The valve actuator operates the stem and disk to control the valve. Depending on the needs of a particular system, several types of actuators are available.

Manual/hand operated actuators take advantage of a handwheel or crank to open the valve. While they are not automatic, they offer the user the ability to position the valve as needed. They find use in remote systems that may not have access to power, but are not ideal for applications that have large valves. For additional mechanical maneuverability, gearheads can adjust open/close speeds.

Electric motor actuators offer manual, semi-automatic, and automatic operation of the valve. This high speed motor is reversible in nature and is utilized for open and close functions. Typically, the actuator is connected through a gear train to reduce the motor speed and increase torque. Meanwhile, the actuator is operated by the position of the valve or by the torque of the motor. Furthermore, a limit switch can be added to automatically stop the motor at fully-open and fully-closed intervals.

Lastly, hydraulic actuators allow for the semi-automatic or automatic positioning of the valve. They are utilized when a large force is necessitated to open the valve, such as a main steam valve. Without fluid pressure, the spring force holds the valve in the closed position. When the hydraulic fluid enters the chamber, the pressure changes. If the force of the fluid is greater than the spring force, the piston moves up, and the valve opens. To close the valve, hydraulic fluid is delivered to both sides of the piston while the other side is drained.


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