Wednesday, July 22, 2015

Valve Selection - Gate Valves

Fluid flow control in industrial processes is most often accomplished through the use of valves installed at specific locations in the piping system to start, stop, throttle, or divert the fluid flow. The application characteristics are broad and varied, resulting in an almost unmanageable menu of possible valve choices. Since we have limited time to spend on any task, it’s useful to employ a simple filter in your valve selection procedure. This generally allows for the elimination of a large group of candidates and allows your efforts to be quickly focused on potentially useful products. One filtering criteria that can be applied to industrial control valves is the valve type.

Valve type generally refers to the means employed to control fluid flow. The closure means and the valve characteristics associated with it can be used to determine whether a valve type may be suitable for your process application. Some common valve types include ball, gate, plug, and butterfly, with numerous variations and customization occurring within each type. Let’s consider the gate valve.

industrial gate valve with hand wheel actuator
Gate Valve With Handwheel
Courtesy WEY Valve
Gate valves have a movable wedge, often rectangular or round, that is positioned in the fluid flow path. This wedge, the “gate” or “disc”, is connected to a stem which extends to the exterior of the valve body. Motion of the stem will position the gate within the valve body to provide some degree of obstruction to the fluid flow path. Fully inserting the gate into the media path will shut off the flow, while successively withdrawing the gate will increase the opening through which fluid can pass and allows for increasing flow rates. Seals are provided along the planar surfaces where the gate contacts the valve body.

What are potential positive attributes of gate valves?

  • When fully open, these valves provide little or no restriction to fluid flow. In addition to having a fluid path cross section generally similar to the connected piping, the valve construction does not impose any change in the fluid flow direction as media passes through the valve. This valve type provides a straight through passage.
  • Gate valves can be employed bi-directionally, with flow control effectively available in both directions.
  • Installation space dimensions along the flow path are generally low, when compared to some other valve types.
  • The energy requirements to change valve position are generally low, since the gate movement is perpendicular to the flow direction.
  • The rate of closure is comparatively slow, inhibiting physical shock (hammering) in the connected piping system.

Here are some other attributes of gate valves.
gate valve with actuator
Gate Valve With Actuator
Courtesy DeZurik

  • As the valve opens, the seals are exposed to the fluid flow. The effects of media velocity and chemical aggressiveness on the seal material may cause deterioration at an unacceptable pace, especially in throttling applications.
  • Gate valve stems generally extend substantially from the valve body, as they must accommodate the mounting of any required actuator and the entire range of motion of the gate. Some installations may not be able to provide the needed space for this arrangement.
  • The slow opening and closing activity of gate valves may not be suitable for some applications.
  • Gate valves are not exceptional at throttling flow. Additionally, attempts at throttling flow may result in gate vibration. There is also concern about premature seal wear due to exposure to higher media velocities while throttling.

Your selection focus may be shifted by these general criteria. Combine your knowledge and understanding of your process and media with the experience and knowledge of valve and control experts to specify a valve configuration that will provide the performance you need.

Wednesday, January 14, 2015

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. 
  • 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.

Tuesday, January 6, 2015

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.