Tuesday, December 17, 2013

Completely Interchangeable Solenoid Valve Coils and Bodies Make Life Much Easier for Your Maintenance Staff

Rotex Solenoid Valves
ROTEX Solenoid Valves with
Completely Interchangeable Coils
ROTEX Controls line of industrial solenoid valves are the best choice for industrial plants today. While the life-time warranty against coil burnout would normally be enough reason (the ROTEX coil is so well designed and the quality is so strong that ROTEX stands behind them unconditionally for their lifetime) the most compelling reason to choose ROTEX solenoids for your plant is their complete coil/body interchangeability.

All ROTEX solenoid valve bodies and coils are interchangeable, allowing for more efficient and less costly inventory. But most importantly, they make it very easy for maintenance crews to quickly change out valves - no matter the area classification or valve type. Other manufacturers’ valves have to be matched, so to be safe, valve and coil are replaced - even when nothing is wrong with one component.

With ROTEX, all that’s needed is the replacement of individual part. This is a greatly appreciated feature, particularly during late night service calls or when searching through storeroom shelves looking for the right part.

Sunday, December 1, 2013

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 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.

Sunday, November 17, 2013

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!

Friday, October 25, 2013

Advantages of Angle Seat Valves

angle valve
ROTEX Angle Seat Valve
The term “angle valve” or “angle seat valve”refers to a family of on-off and control valves that have a “Y” pattern body style, and use linear action to lift a piston off a seat to open and close the valve, while providing a very tight shutoff. By having the seat on an angle, the piston can be pulled out of the flow path, eliminating its obstruction, and therefore provide maximum flow. These valves are known for their large flow rates, they can operate with zero differential pressure and with high process media temperatures. Additionally, it’s a good choice for fluids with higher viscosities and also with dirty process media. They are an excellent choice for water and steam. Angle valves are also a good choice in hazardous areas when the accompanying pilot valve is located outside of the hazardous area.

Thursday, October 17, 2013

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.

Friday, October 11, 2013

What are NAMUR Mount and Pipe Mounted Solenoid Valve Mounting Styles?

NAMUR Mount Solenoid
When selecting a solenoid valve for valve automation, the preferred mounting method needs to be considered. The two most common choices available are "NAMUR" mount and "PIPE" mount.

NAMUR on Actuator
NAMUR mount solenoids use a standardized "sub-plate" which months directly to the actuator on one side and to the solenoid valve on the other. This adaptor allows for quick change-out and minimizes the amount of plumbing required and is therefore less expensive to install.

Pipe Mount Solenoid
Pipe mount solenoids use the supply piping for support and mounting. Pipe mount solenoids are less compact and require more effort to service, but can be installed on any system as you are not limited to a pre-existing pattern and have more selection in valve size.
Pipe Mount on Actuator

Wednesday, October 2, 2013

Industrial Valve Limit Switches

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. 

Tuesday, September 24, 2013

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.

Thursday, September 19, 2013

What is a Rack & Pinion Actuator?

According to Wikipedia, "A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby translating the rotational motion of the pinion into the linear motion of the rack."

Image courtesy of Wikipedia

When applied as a pneumatic valve actuator, opposing racks are attached to pistons in a cylinder. When one side is pressurized, the pinion bearing turns in one direction. When air or spring tension is applied to the opposite side, the pinion bearing turns in the other direction, thus allowing rotational motion in both directions.
ROTEX Rack and pinion actuator
Transparent actuator showing opposing pistons (ROTEX)

rack and pinion bearing
Pinion bearing and rack with piston and seal (ROTEX)
Housing which forms outer pneumatic cylinder walls (ROTEX)
Advantages of pneumatic rack and pinion actuators are compactness and space savings, reliability, durability and life cycle. Disadvantages are gear and bearing wear, piston seal fatigue and stem seal leakage.

Here is a great article on rack and pinion actuators from Valve Magazine.

Wednesday, September 18, 2013

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

Thursday, September 12, 2013

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.

Friday, September 6, 2013

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.

Tuesday, September 3, 2013

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.