Showing posts with label scotch yoke. Show all posts
Showing posts with label scotch yoke. Show all posts

Features of the ROTEX DRS Scotch Yoke Actuator

...
Actuator Modules 
  • ROTEX actuator spring modules and pneumatic modules can be removed, swapped, rebuilt, or reinstalled on the frame module without disassembling the frame module. No need even to remove top cover of frame module, because all bolting for removal of the modules is external. 
  • Actuators can easily be changed in the field from fail close to fail open by just swapping the positions of the spring and pneumatic modules. No need to dismantle the frame cover or cylinder assembly. 
  • Actuators can be modified from double acting to spring return easily in the field by adding a spring module. 
Springs are lifetime lubricated and epoxy coated.
  • Springs are pre-compressed inside their welded spring modules for safety and ease of use.
  • Pneumatic cylinders are lined with hard chrome plating. Smooth to eliminate wear of piston seals, the surface is very hard, for long life. 
  • Inside the pneumatic module, dual oversized tie rods are protected from external corrosion. Where the tie rods pass through the piston head, ROTEX has improved the design by providing a slide bearing, where most designs don’t. This bearing is important to help maintain alignment and assure smooth operation. 
Frame Module
  • Inside the frame module, the yoke is supported by life time lubricated bearings. Needle roller bearings ensure the most efficient torque transmission. 
  • Extra heavy duty travel adjustment bolts allow for +/- 10% adjustment of the 90 degree stroke. The area of contact is large, to withstand the impact forces. 
  • The yoke thrust pin is made of case hardened steel to resist wear. 
  • The piston shaft is supported on each side of the frame module by solid bearings that ensure proper alignment and smooth operation. 
Flexijoint
  • Each piston shaft of the ROTEX DRS is equipped with two Flexijoints. These specially designed joints compensate for movement and changes in alignment to reduce internal stresses and increase output torque. 
  • The thrust transmitted through the Flexijoints ensures no side thrust on the cylinder walls and bearings. 
Unique Sealing Features
  • Piston seal is ROTEX X design. Flexibility of the sealing material reduces friction, prevents leakage, and extends actuator life. The X shaped seal is wear compensating, and the unique shape of the seal retains the grease for longer periods. The piston is guided by a PTFE thrust bearing, which helps keep the piston centered, and seal wear to a minimum. 
  • The tie rod seal is also of the ROTEX X design. Old fashioned O-rings are replaced by these flexible, low friction, resilient seals to reduce the failure rate of tie rod seals. Also reduces the wear and tear to the tie rods themselves. 
  • ROTEX has also replaced the standard O-ring of the shaft seal. In this position, we provide a proven V-seal design. This self-energized, wear compensating seal guarantees low hysteresis and minimum friction. Like the X seal of the piston and tie rod seals, the inherent shape of the V-seal helps keep the grease where it needs to be. 
Optional Hydraulic Override
  • ROTEX DRS actuators may be ordered with an optional hydraulic override, or the override may be retrofitted to an existing actuator. 
  • The override is fitted into the spring cartridge, to keep the overall dimensions of the actuator and override to a minimum. Can withstand up to 2,000 psi hydraulic pressure.
  • Easy to operate.
  • Special Z seal ensures zero leakage and extended life.


ROTEX Pneumatic Valve Actuator Introduction

...
Here is a movie/slideshow introducing the ROTEX family of pneumatic valve actuators. The movie includes the ECV "Infinity line of rack and pinion actuators, the DRS scotch yoke series and the DRC and DRV large scale rack and pinion series.

Unique design and high performance features are explained and pictures of automated valve packages are included.


Intro to ROTEX Solenoids, Valve Actuators and Limit Switches

...
Introduction of ROTEX Controls product line of solenoid valves, Infinity ECV line of rack and pinion actuators, DRS and DRV scotch yoke actuators, and HYV hydraulic actuators and limits switches.

ROTEX offers a range of Solenoid Valves and Air Operated Valves used for handling almost any fluid with various of temperature, pressure or vacuum for use in Control and Automation applications.

ROTEX limit switches are designed to last and meet your required service conditions. Both the weather proof and explosion proof switches feature an aluminum die cast enclosure that is powder coated for superior corrosion resistance resulting in a weather proof enclosure to IP67. Stainless steel enclosures are available, also confirming to IP67.

Valve Actuation 101: Comparative Review of Pneumatic Actuators and Advantages of Rack and Pinion

...
Here's is a good presentation on the various types of industrial pneumatic valve actuators, such as scotch yoke, vane, diaphragm and rack and pinion, and their respective advantages and disadvantages.



Watch a Pneumatic Scotch Yoke Actuator with Hydraulic Manual Override in Action

...
An interesting demonstration of a ROTEX DRS high performance scotch yoke pneumatic actuator mounted on a large ball valve. Video shows actuator opening valve, closing valve, the valve position indicator, the hydraulic manual override and manual hydraulic pump.  Good visual education for those who never saw a large valve and a large actuator.


For any new engineer involved in process control, beginner valve technician, sales or service professional or newbie to the valve industry, here is a helpful 7 minute video on how scotch yoke valve actuators are designed and constructed.

While this video outlines how ROTEX Controls builds their actuators, the video gives you a good general idea of the construction and major components.

ROTEX is a a recognized worldwide leader in manufacturer of valves actuators and valve accessories.

Actuators 101: Quarter-turn Pneumatic Actuator Types

...
Pneumatic valve actuators come in two basic types: rack & pinion and scotch-yoke. Both style actuators provide 90 degree rotational torque to drive a quarter-turn valve (ball, plug, butterfly) open or closed.

The scotch-yoke actuator uses a piston, which moves a linear push rod that in turn engages a pivoting lever arm to provide rotation. A rack & pinion actuator uses opposing pistons with gears to engage a pinion gear shaft. The practical difference however is in size, power, torque curve and ease of adding peripherals.
rack and pinion actuator
Rack & Pinion

Rack & pinion actuators tend to be more compact, have standardized mounting patterns and have an output torque range suitable for small to medium sized valves. They include standard bolting and coupling patterns to directly attach to a valve, solenoid, limit switch or positioner.



scotch yoke actuator
Scotch-yoke

Scotch-yoke actuators, for the most part, are much larger than rack & pinion actuators and consequently provide much higher torque output. These actuators are most often used on large quarter turn valves and require careful attention to the mounting requirements because of their power.

Both styles come in either "direct acting" or "spring return" versions. Direct acting actuators use the air supply to move the actuator in both directs (open and close). Spring return actuators, as the name implies, uses springs to move the actuator back to its "resting" state.

Fire-Safe Scotch-Yoke Actuators with 3 Second Operation

...
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!

Proper Actuator to Valve Torque Sizing

...
pneumatic actuator torque chart
A quarter turn pneumatic actuator, wether direct acting or spring return, has a given output torque based upon the air supply pressure provided. This output torque can be fairly linear, or very non-linear depending on the style of the actuator (rack and pinion vs. scotch yoke) or if the application calls for springs to be used for opening or closing.

It is critically important to properly select and match the design and torque requirements of the pneumatic actuator and the valve in any given process. Improper selection will result in failure, much higher installed cost, not to mention lost production.


There are two main ways an improperly sized actuator costs money. If the actuator is too small (underpowered at a given line pressure to provide ample seating and unseating torque), it will fail and need to be replaced. If an actuator is severely oversized, the cost of the actuation package is higher, and space is wasted accommodating the larger physical size.

Many actuator failures result before the valve and actuator are even installed because of improper sizing. Proper application engineering calls for proper use of safety factors.

A safety factor is applied when sizing a pneumatic actuator. These recommended safety factors vary slightly from manufacturer to manufacturer. However, applying a safety factor is not enough. Special consideration for the valve torque curve from fully closed to fully open must be evaluated. After the valve full-stroke torque is known, then the actuator torque curve should be evaluated side by side to assure that the safety factor exceeds all point of the valve torque curve. Otherwise, an accidental "dead-zone" where the actuator torque curve is inadequate to move the valve at a certain part of the valve stroke can happen.

Obviously, its not a good idea to apply an actuator with too small a safety factor. These actuators can add maintenance costs due to erratic operation or a higher likelihood of failing all together.

Quarter turn valves and actuators are often used in demanding application requiring high cycle rate, exposure to harsh environments and / or control critical processes such as hazardous chemicals. For these reasons a great deal of attention and care must be given to proper sizing. If you're unsure about any given application, make sure you contact an expert who can help you.

Advanced Scotch Yoke Design Increases Service Life

...
ROTEX recently replaced some old "orange" scotch yoke actuators with the DRS series. The customer is a major international producer and marketer of food and agricultural products.  The "orange" actuators were experiencing high wear and had to be rotated out and serviced every few months. After the ROTEX DRS actors were installed, at last count, they had 125,000 cycles without any internal corrosion or degradation.

Let's examine the design improvements that allow this superior performance:
  • Pneumatic cylinders are lined with hard chrome plating. Smooth to eliminate wear of piston seals, the surface is very hard, for long life.
  • Springs are lifetime lubricated and epoxy coated.
  • Inside the pneumatic module, dual oversized tie rods are protected from external corrosion. Where the tie rods pass through the piston head, ROTEX has improved the design by providing a slide bearing, where most designs don’t. This bearing is important to help maintain alignment and assure smooth operation.
  • Inside the frame module, the yoke is supported by life time lubricated bearings. Needle roller bearings ensure the most efficient torque transmission. The piston shaft is supported on each side of the frame module by solid bearings that ensure proper alignment and smooth operation.
  • Each piston shaft of the ROTEX DRS is equipped with two Flexijoints. These specially designed joints compensate for movement and changes in alignment to reduce internal stresses and increase output torque. The thrust transmitted through the Flexijoints ensures no side thrust on the cylinder walls and bearings.
  • Piston seal is ROTEX 3X design. Flexibility of the sealing material reduces friction, prevents leakage, and extends actuator life. The 3X shaped seal is wear compensating, and the unique shape of the seal retains the grease for longer periods. The piston is guided by a PTFE thrust bearing, which helps keep the piston centered, and seal wear to a minimum.
  • The tie rod seal is also of the ROTEX 3X design. Old fashioned O-rings are replaced by these flexible, low friction, resilient seals to reduce the failure rate of tie rod seals. Also reduces the wear and tear to the tie rods themselves.
  • ROTEX has also replaced the standard O-ring of the shaft seal. In this position, we provide a proven V-seal design. This self-energized, wear compensating seal guarantees low hysteresis and minimum friction. Like the X seal of the piston and tie rod seals, the inherent shape of the V-seal helps keep the grease where it needs to be.

In 13 months, the ROTEX DRS went 125000 cycles without internal corrosion nor significant wear.

What is a Scotch Yoke Pneumatic Valve Actuator?

...
According to Wikipedia, "The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed."
Animation of Scotch Yoke (courtesy of Wikipedia)

In a pneumatic actuator, the scotch yoke mechanism converts linear motion (provided by an air supply and pistons) to rotary motion. A return spring sets the rotation in the opposite direction.

Diagram of Scotch Yoke Internals (courtesy of ROTEX Controls)


Scotch yoke mechanism provides a great torque curve for many valve types and are most often used on larger valves. Additionally, as valve torque requirements increase, a scotch yoke actuator becomes a more economical choice considering production cost.

The disadvantages of scotch yoke actuators are typically the wear and tear on the pin and bearing mechanism. Manufacturers like ROTEX Controls have reduced this issue with innovative design improvements that reduce friction and wear.
ROTEX Controls DRS Scotch Yoke Actuator


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

...
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.

Gas Over Oil Actuators for High Pressure Gas Lines

...
ROTEX Gas over oil
Gas Over Oil Actuator
Gas Over Oil actuators are used on gas transmission lines where there is sour gas (Hydrogen Sulphide) present. Because of the lack of electricity or other energy sources in remote locations, the pipeline gas is used as the energy source for the actuator, isolating the corrosive gas gas from the wetted parts of the actuator with hydraulic oil.


With the hydraulic oil energized by the pipeline gas, these actuators can operate with gas pressures up to 2000 PSI and are typically used in tandem with scotch yoke actuators (in ROTEX case the DRS, DRV, HYV or any other make of actuators). The hydraulic oil bathes the internal actuator mechanism, preventing the internal corrosion, and providing maintenance-free, high cycle and long life.

Gas-Over-Oil include a secondary storage tanks for up to 3 additional operations, in case of loss of the primary gas supply. The actuators can be used to power 1/4 turn actuators, or linear actuators for rising stem valves.

Gas over oil actuators general features include:

  • Line break control integrated with manual reset function. On exceeding the leak rate, the LBC valve operates shutdown valve and closes the main valve. Requires manual reset.
  • Torque control ensures that the actuator does not exceed the maximum seal torque for stem can be supplied. 
  • Manual hand pumps.
  • Gas filtration and dehumidification.


Defining a "Quick Acting" Pneumatic Actuator

...
ROTEX Fast acting actuator
The desired speed of the pneumatic actuator opening or closing is a consideration of the application itself. For applications where an open valve may feed a fire, or overfill a tank, quick closing is required. Conversely, there are times when lines or tanks need to vented very quickly, or processes must be diverted quickly, and a fast opening actuator is applied.


Pneumatic Actuators can vary in opening and closing speed, depending on air supply, venting orifice, and/or size spring involved. A very general statement of valve actuator opening/closing times is normally in the "tens of seconds" whereas fast acting actuators open or close typically in less than 5 seconds.

The engineering of quick acting actuators must be done by seasoned professionals who fully understand the process. Other considerations when applying fast acting actuators are redundancy, failure mode (loss of energy supply), media, criticality and size.

Picture courtesy of Rencor Controls.