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.