Showing posts with label fail close. Show all posts
Showing posts with label fail close. Show all posts

Fire-Safe Scotch-Yoke Actuators with 3 Second Operation

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ROTEX Scotch Yoke
Critical Service Valves with
ROTEX DRS Scotch Yoke
A Central American power generation company needed 10" and 16", Class 900, triple-offset, critical service butterfly valves to operate flawlessly and quickly in the event of fire or loss of air supply.  They chose ROTEX Controls double acting DRS Scotch-Yoke actuators with hydraulic overrides.

The actuator package also specified a (5) second or less close time, a fusable link for emergency close in the event of fire, a declutchable manual override, and ASME air receiver tanks for "fail mode" that would allow for (2) full operational cycles.

ROTEX Controls engineers also included a 3-way fusable link that supplied air to a pilot operated shuttle valve. If the system was exposed to fire, the fusible link will fail, venting the air feed to the pilot causing the shuttle valve to shift and energize the actuator.

The result was an actuator that closed the valve in under (3) seconds. Additionally, the automated packages were delivered on time and under budget!

Industrial Valve Limit Switches

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ROTEX Limit Switches
In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve actuator. They are used to show the open or closed position of an industrial valve, or as safety interlocks to protect man or machine. The enclosure is usually classified in NEMA (National Electrical Manufacturers Association) Standards, such as NEMA 4, NEMA 4X or NEMA 7 (explosion resistant).

ROTEX Limit Switch
Internal Mechanical Limit Switch
The internal switches can be electromechanical or magnetic. Electromechanical switches respond to a mechanical cam on a shaft to change state (make or break electrical contacts). Magnetic switches use a magnetic field to change state in a reed switch, or  to sense a disruption in the magnetic field, or through capacitance.

ROTEX Limit Switch
Internal Magnetic Limit Switch
Along with an electrical signal, visual indication is an important part of a limit switch. Most switch come standard with a "dome" or "beacon" displaying "open" or "closed" or positions anywhere in between.

When applying limit switches on industrial valve application one should consider the following:


  1. Environment - is the limit switch in an area where there may be dust, spray-down, rain, corrosive gasses, combustible gases, or require sanitary conditions. Choosing the correct NEMA classification is critical.
  2. The electrical rating of the signal being transmitted. AC or DC? High voltage or low?
  3. Operation Frequency and Cycle life - will the switch only open/close occasionally, or will it cycle every few seconds? Mechanical switches have inherently shorter cycle lives than do proximity or magnetic switches. Choose the best switch considering load and cycle life.
  4. Visual indication - do you need to see the valve status from a distance? 
  5. Auxiliary outputs - besides opening of closing the primary signal, are their other signals you must send by using additional switches in the housing. 


Critical Service, Triple Off-Set Metal Seated Butterfly Valves with ASME Supply Tank, Fusable Links and Manual Hydraulic Over-Ride

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16" & 10 " Triple Off-set Valves automated block valves. These are pneumatically operated valves with ASME air tanks for fail close operation on loss of electrical signal. Also included are manual hydraulic over-ride cylinders and spring loaded 3-way diverter valves with "fusible links.


After installation of valve in to pipe line, plant air is supplied to the tank inlet valve. A pipe from the tank outlet to the actuator  with filter and regulator provides the actuator clean, regulated supply air.

All electrical connections for limit switch and solenoid valves are terminated in the limit switch housing.

Valve are supplied with small 3-way ball valves with fire-safe "fusible" links and spring loaded handles that will close the valve in the event of a fire.

The manual hydraulic over-ride is used in case of loss of air, or loss of electric. 6 foot and 15 foot hydraulic lines are used to supply the hydraulic cylinders power and must be connected of the valves will not function.

As designed, these valves open in under 5 seconds and close in 1.6 seconds, have the ability to be manually over ridden in the event of a loss of air or electric, and have fire-safe spring loaded links to close the valve in the event of a fire.