Showing posts with label process control valve. Show all posts
Showing posts with label process control valve. Show all posts

Thursday, March 15, 2018

Installation Basics for Ball Valves

three piece industrial ball valve
Three piece industrial ball valve, manually operated
Image courtesy of Duravalve, Inc.
Ball valves are characterized by their closure mechanism. Most often, a ball valve has a spherically shaped fabrication (ball) that is inserted in the fluid flow path. The ball has an opening through its center, often circular in cross section and matching the diameter and shape of the connected pipe. The ball is contained within the body of the valve and rotated around its central axis by torque applied to the stem. The stem, which extends through a seal to the exterior of the valve body, can be manually or automatically controlled via several methods.

During valve operation, the ball is rotated through a ninety degree arc from a fully closed to fully open position. When fully closed, the opening in the ball faces the sidewalls of the valve body and is cut off from the fluid by seals that secure the ball in place and prevent fluid flow around the ball. As the valve stem is rotated toward the open position, the cross sectional area of the opening is increasingly exposed to the fluid flow path until the open area through the ball is aligned with the flow path in the fully open position.

Here are some general installation and removal guidelines for ball valves.

  • Verify whether the valve is unidirectional or bidirectional. If valve function is limited to a single direction, make sure the inlet and outlet ports are properly oriented to the piping system flow direction.
  • Adequate access for handle movement, along with an operator's hand, should be confirmed prior to installing the valve.
  • Ball valves will function in any orientation.
  • If automated with an actuator, maintain sufficient clearance around the valve and actuator to provide adequate maintenance access.
  • Keep the installation area free of debris and dirt. Protect any valve parts that are removed or are awaiting installation. Avoid introducing any foreign matter, dirt or debris into the valve.
  • Valves may have any of a number of connection methods, including threaded, flanged, or socket weld. Disassembly of the valve may be appropriate when installing some types, especially socket weld. Care should be taken to avoid any damage to the ball surface, seals, or sealing surfaces. Scratches and nicks can produce leakage when the valve is reassembled.
  • If disassembling a currently installed valve, verify that the piping system is not under pressure prior to starting. Cycle the valve through open and closed positions a couple times to relieve any pressure that may be retained in the valve body.
  • Follow all manufacturer recommendations for applied torque on any fasteners.
  • When a ball valve is disassembled, for any reason, it may be a good time to replace seats.
  • Leak check final installation. Tighten packing gland nut to eliminate leaks at the stem.
These are general recommendations. In every instance, a review of the valve manufacturer's specific instructions prior to starting installation or service is good practice. Share your fluid control challenges with industrial valve specialists. Leverage your own knowledge and experience with their product application expertise to develop effective solutions.

Friday, January 5, 2018

One, Two, or Three Piece Ball Valve?

one piece, two piece, and three piece ball valves
Examples of one, two, and three piece ball valves.
Image courtesy Duravalve
Ball valves are employed throughout many commercial, institutional, and industrial venues where the need to isolate part of a system is necessary, or even just to regulate the on/off condition of system fluid flow. The product variants are almost uncountable, with a version to accommodate almost any application.

When selecting a ball valve, one facet of construction will be evident in your research. There are three common types of ball valve construction; one piece, two piece, and three piece. Here are some general considerations and differences among the three types.

  • A one piece ball valve has a body and end connections formed from a single piece of material. This construction presents a comparatively reduced number of opportunities for leakage. The valve trim and seals are inserted through one of the end connections. This type of valve will not have a port size equal to the line size. The simplicity of the one piece body design tends to make their cost lower than the other versions. Once the valve is in place, it cannot be serviced without removing the entire valve assembly from the piping system.
  • Two piece ball valves generally have one piece that includes an end connection and the body, plus a second piece that fits into the first that will hold the trim in place and provide the second end connection. The construction presents an additional leak potential where the two pieces are joined, but also allows disassembly of the valve for replacement of the internals. These valves can provide full port service and bidirectional flow shutoff.
  • A three piece ball valve essentially separates the connection portions of the valve assembly from the body of the valve. These will be more expensive than either of the other two types, but their allowance for removing the valve body and trim from the piping system while leaving the connections in place may prove valuable for many applications. Full port and bidirectional shutoff can be provided by this construction.
Properly applied, all these valves will provide good service. Your selection depends on the demands of the application. Share your fluid measurement and control requirements and challenges with process control specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Monday, May 22, 2017

Two New Products From SVF Flow Controls

rack and pinion actuator and butterfly valves
New products from SVF Flow Controls
SVF Flow Controls, manufacturer of valves and actuators for industrial process control (learn more here), recently released their new rack and pinion actuator, the EZ-Tork™. The line of pneumatic valve actuators features bi-directional stroke adjustment, a continuous position indicator, hard anodized aluminum housing, and universal mounting. The line offers 33 models spanning a broad range of operating torque. Units are available in double acting or spring return variants.

The SL Series of butterfly valves feature direct mounting for electric or pneumatic automation. Manually operated units have a ten position locking handle or gear operator. Epoxy coated ductile iron body, 316 stainless steel disc, and EPDM or BUNA seats enable the application of this valve throughout many industrial settings. Sizes range from 2" to 12".

More detail is available from valve and fluid control specialists. Share your application challenges and combine your own process knowledge with their product application expertise to develop effective solutions.

Wednesday, July 27, 2016

Hayward Announces New Electric Valve Actuator Line

electric valve actuators with manual override
New HRS Series Electric Valve Actuators
Courtesy Hayward Flow Control
Hayward Flow Control issued a press release in early June announcing the introduction of its HRS Series of quarter turn electric valve actuators. The actuators complement the company's companion lines of fluid process products, including thermoplastic valves, strainers, filters, controls, bulkhead fittings and tank accessories, and corrosion resistant pumps.

The new HRS line provides practical features and benefits to users.
  • Product torque range from 300 in-lb to 177,000 in-lb
  • Aluminum housing with powder coat
  • Double square drive socket, ISO5211 compliant mounting
  • On/Off or Proportional Control  with 2-10 vdc or 4-20 ma inputs and outputs
  • NEMA 4/4X/IP67 enclosure rating
  • Range of available AC and DC voltages
  • Integrated local control station
  • Visual position indicators
  • CSA Certified, UL439
  • Two Year Warranty
There are numerous variants that can be configured using base models and available options. For more detail, contact a product specialist. Share your fluid process control challenges with them, combining your process knowledge with their product application expertise to produce the most effective solutions.


Monday, February 29, 2016

New Metal Seated Ball Valves Introduced

Cutaway view of metal seated industrial ball valve SVF Flow Controls
Cutaway view of a metal seated ball valve
Courtesy SVF Flow Controls
Ball valves are utilized across a wide range of industrial process fluid flow control applications. Consequently, there are many ball valve variants, each designed to satisfy a particular range of application requirements.

Reviewing some of the attributes of ball valves that might make them the best choice:
  • Tight closure.
  • Very low resistance to flow.
  • Best suited for applications requiring fully closed or open control.
  • 90 degrees of rotational motion from open to closed position yields rapid response.
  • Comparatively compact, without the space requirement for extending stem movement as required by some other valve types.
  • Wide range of construction materials for the body, stem, ball, and seals.
  • Moderate force required for actuation.
  • A full size port provides for very low pressure drop across the valve when fully open.
  • Requirements for maintenance are generally low. 
  • No lubrication required.

One limiting factor for the application of ball valves, as with many other valve types, is the seat material. Most often, seats are fabricated from elastomeric or other "soft" materials. While these materials provide good sealing performance, their inability to withstand higher fluid temperatures makes them unsuitable for some industrial applications. To satisfy a wider range of process applications, some manufacturers offer metal seated ball valves. The metal seated valves are designed to meet severe service applications involving high temperature, erosive fluids and other challenging shutoff requirements where soft seats would rapidly deteriorate.

One manufacturer, SVF Flow Controls, provides metal seated ball valves in sizes 1/2" through 12" with a full port design. Because of their intent for severe service applications, metal seated ball valves are generally provided with other design features that enable their application across a wide range of high temperature or erosive fluid applications.

I have included a data sheet below that provides additional technical information, or you may contact a valve application specialist for any assistance you need. Share you fluid control challenges and get effective solutions.


Wednesday, January 27, 2016

Cavitation Induced by a Control Valve - Demonstrated



Consider a generic industrial fluid process control operation. There are pumps, valves, and other components installed in the process lines that, due to their interior shape or their function, cause changes in the fluid motion. Let's look specifically at control valves and how their throttling operation can create conditions able to greatly impact the valve itself, as well as the overall process.

Fluid traversing a control valve can undergo an increase in velocity when passing the constriction presented by the valve trim. Exiting the trim, fluid then enters the widening area of the valve body immediately downstream with a decrease in velocity. This change in velocity corresponds to a change in the kinetic energy of the fluid molecules. In order that energy be conserved in a moving fluid stream, any increase in kinetic energy due to increased velocity will be accompanied by a complementary decrease in potential energy, usually in the form of fluid pressure. This means the fluid pressure will fall at the point of maximum constriction in the valve (the vena contracta, at the point where the trim throttles the flow) and rise again (or recover) downstream of the trim.

Here is where cavitation in control valves begins.

If the fluid being throttled is a liquid, and the pressure at the vena contracta is less than the vapor pressure of the liquid at the flowing temperature, portions of the liquid will spontaneously vaporize. This is the phenomenon of flashing. If, subsequently, the pressure of the fluid recovers to a level greater than the vapor pressure of the liquid, any flashed vapor will rapidly condense, returning to liquid. This collapse of entrained vapor is called cavitation.

Flashing, the generation of vapor bubbles within the liquid, will precede and set the stage for cavitation. When the flashed vapor bubbles condense to liquid they often do so asymmetrically, with one side of the bubble collapsing before the rest of the bubble. This has the effect of translating the kinetic energy of the bubble’s collapse into a high-speed “jet” of liquid in the direction of the asymmetrical collapse. These liquid “microjets” have been experimentally measured at speeds up to 100 meters per second (over 320 feet per second). What is more, the pressure applied to the surface of control valve components in the path of these microjets can be intense. An individual microjet can impact the valve interior surfaces in a very focused manner, delivering a theoretical pressure pulse of up to 1500 newtons per square millimeter (1.5 giga-pascals, or about 220000 PSI) in water. In an operating fluid system, this process can be continuous, and is known to be a significant cause of erosive wear on metallic surfaces in process piping, valves, pumps and instruments. As the rapid change in pressure takes place, the bubbles (voids in the liquid) collapse (implode), and the surrounding metal surfaces are repeatedly stressed by these implosions and their subsequent shock waves.

Consequences for control valves, as well as for the entire control process, vary and are often destructive. They may include:
  • Loud noise
  • Strong vibrations in the affected sections of the fluid system
  • Choked flow caused by vapor formation
  • Change of fluid properties
  • Erosion of valve components
  • Premature destruction or failure of the control valve 
  • Plant shutdown
The video provides a visual demonstration, through clear piping, of what happens inside the piping system when a valve is operated in a manner that causes substantial cavitation.

The solution lies in minimizing the potential for cavitation to occur through proper valve selection and sizing, along with coordinating operating characteristics of pressure drop inducing components with the total system performance. One valve manufacturer's recommendations are summed up in four basic approaches.

  • Avoidance of cavitation through proper valve selection. Use a valve with a rated liquid pressure recovery factor greater than that required for the application. Some applications may be suitable for the use of an orifice plate downstream of the valve.
  • Cavitation Tolerant Components capable of withstanding limited amounts of cavitation without excessive wear. Increased flow noise is likely to accompany this route.
  • Prevention of cavitation through the use of valve trim design that reduces pressure in several steps, avoiding excessive flashing. These valves can be expensive, but their effectiveness makes them an alternative worth considering.
  • Containment of the harmful effects of limited to moderate cavitation through trim designs that eliminate contact of the fluid with metal surfaces which are more susceptible to damage.

Share your requirements and application challenges with a valve specialist and gain insight through their recommendations. Combining your process knowledge with their product application expertise will yield a great solution.

Wednesday, January 6, 2016

Fluid Flow Control - Slurries, Entrained and Suspended Solids

Slurry, suspended solids in fluid, toxic fluid
Industrial process control can be confronted with
hazardous, corrosive, or other fluids containing
suspended solids.
Industrial process control can involve the manufacture, storage, or transport of almost any imaginable fluid. Media can range from water to concrete, hydrogen gas to steam, and anything in between or outside of those boundaries. Valves are the favored control device for regulating fluid flow and they are available in uncountable varieties, each with particular aspects making them more of less suitable for a particular media or application.

Most industrial valves consist of a body, a stem, and some form of flow obstruction which is located within the media flow path. Operation of the stem repositions the obstruction to allow or block the flow. All of these valve types have a defined sealing surface where the obstruction contacts the body. They also have additional seals where the stem penetrates the body. These design features, while providing certain functions and application advantages, also add to the operational complexity and parts count for the valve.

There is a valve type with a simple operating principle that provides superior performance when the application involves certain media characteristics. It is called a pinch valve, and here is where it excels.

  • Resistance to abrasion and corrosion from slurries or fluids containing suspended solids and the ability to provide tight shutoff around particulates
  • Media and environmental temperature range -40 deg F to +300 deg F
  • Low to moderate operating pressure
  • Flow regulating capability and tight shutoff
  • Non clogging
  • Straight through full bore design with minimal flow resistance
  • Isolation of the valve body and workings from the media
  • Low parts count, low maintenance, easy repair/replacement
cutaway view of manually operated industrial pinch valve
Cutaway view of manually
operated industrial pinch valve
A pinch valve consists of a sleeve, through which fluid flows, and a means to compress or "pinch" the sleeve to reduce the open area inside the sleeve. The sleeves are most often fabricated from elastomers with various types of fiber reinforcement. Closure is commonly achieved through movement of one or two bars to squeeze the sleeve, providing throttling or positive closure. The flexibility of the sleeve material allows for tight shutoff, even with fluids containing suspended solids. The valves can be coupled with electric or pneumatic actuators and are available with industry standard connections. One valve variant has a body that can be pressurized to close the sleeve, without the need for a separate actuator. Pinch valves are available with and without an enclosing body.

You should be familiar with the capabilities and forms of this unique valve type. When confronted with certain application challenges, a pinch valve can be a superior solution. I included a product line data sheet from one manufacturer, General Rubber Corporation, so you can see all the different variants that are available. You can get even more information, or start a conversation about any of your process control challenges, by contacting a product specialist.