Cowan Connection

Latest News from Cowan Dynamics

Why Use a Valve Actuator Limit Switch?

Why use a valve actuator limit switch? Valve automation is not simply the selection of the actuator. Control components are a big part of the complete actuation assembly.  When looking into the components that a valve automation system must have, we normally see solenoid valves which are used to control the pressurized fluid into the actuator. In addition, we also see what we often call position limit switches.  A valve actuator limit switch is a device that is designed to provide a remote signal to the control station, also known as PLC or DCS, regarding the valve position, often open or closed.  They can also be set to provide different position indications depending on the application. The switch will provide a signal on the position once the valve reaches it, therefore there will be...

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Knife Gate Valve Actuator

Knife gate valves are linear valves in which the closing membrane is a gate that is sharpened to better cut through the process media (such as slurry). The gate is connected to a stem and travels inside the valve body in which scrappers are often included to clean the gate as it moves from open to closed. They can be manual or automated, with metal or resilient seats, bi-directional, and come in wafer, lug and flange connections. Knife gate valves are very versatile and can be used in both isolation and control applications.  However, to provide good control characteristics the valve trims must be custom-made. Conventional resilient and metal seated knife gate valves are designed primarily for fluid isolation as they have poor control characteristics. Their ‘blade-like’ gate design makes...

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Butterfly Valve Actuator

Butterfly valves are rotary or 90-degree valves where the closing membrane is a disc that is connected to the stem perpendicularly either symmetrically or asymmetrically. They can be manual or automated, with metal or resilient seats, bi-directional, and come in wafer, lug, and flanged connections. Butterfly valves are very versatile and can be used in both isolation and control applications. However, their control capabilities are limited. Conventional resilient seated butterfly valves are designed primarily for fluid isolation as they have poor control characteristics. The seat is an elastic single piece that holds in place the valve body. This design can have its integrity compromised if the valve is kept partially open. For this reason, butterfly valves that are designed for control...

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What is a Valve Signature & How It Effects Actuator Sizing

A valve is a pressure vessel with internal moving parts; and when they move, they encounter resistance from other parts and from the flow. The recording of the pressures and forces associated with overcoming these resistances can be referred to as “valve signature”.  For actuator sizing, it is critical to obtain accurate valve thrust/torque data. This is especially true for spring-return actuators as conservative or exaggerated valve thrust/torque data can lead to extremely oversized and expensive actuators. The thrust or torque required to move the valve, in either direction, will vary throughout its stroke. In industry, the following  terms are used to describe the various data points required for actuator sizing: (fig.1 - see table for details) The thrust or torque...

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What is a Scotch Yoke valve actuator ?

Scotch yoke valve actuators are 90˚ driving mechanisms that can be powered by compressed air or hydraulic oil from an external source. Why consider a Scotch yoke valve actuator? Deciding which actuator is best for a certain application depends on several factors like environment, required accuracy, and close/open speed. When choosing between a 90˚ actuator such as a Rack & Pinion or Scotch Yoke, the main difference between these actuators are the torques they can generate. The following table shows the difference between the two main types of 90˚ actuators: How do they work? A scotch yoke actuator typically consists of a crank and piston system in a hollow cylinder. Pressure is applied to a side of the piston inside the cylinder. As a result, force is generated which...

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Valve Actuators

Valves are used to control the flow of fluids in process control applications by opening, closing, or partially obstructing the fluid flow and controlling the line pressure. Depending on the flow requirements of the process system, some method of changing the positions of valves is needed. Some valves are operated with hand wheels or levers. Other valves must be open, closed, or throttled frequently. Manually positioning valves in these types of situations is not practical and instead of using hand wheels or levers to control actuation, automated valve solutions such as valve actuators are used to position the valves. What is a valve actuator? A valve actuator is defined as a mechanical device that moves or controls a device such as a control valve. Actuators reduce the need for...

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Featured Valve Automation Actuators

A Series Feature

Designed and engineered for severe-service applications, the A Series bore sizes range from 4” to a whopping 42” diameter. We also offer a wide range of automation options.

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AS Series Feature

Next-generation “compact” model provides a shorter and lighter canister for installations where space is a premium.

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ML Series Feature

Our ML Series Double-Acting Hydraulic Valve Actuators are designed to suit a wide range of applications; from commodity to severe-service extremes.

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