Showing posts with label Jamesbury. Show all posts
Showing posts with label Jamesbury. Show all posts

Sunday, September 15, 2019

What is a Ball Valve?

Ball valve cutaway
Cutaway of specialized ball valve with characterized
ball for control valve applications. (Neles)
A ball valve is a 90 degree rotational motion valve that uses a metal or ceramic ball with a hole through its center to stop or start fluid flow. The ball, shown below in Figure 1, opens and closes to allow fluid flow through the ball valve. When the valve handle or stem is turned to open the valve, the ball rotates to a point where the hole in the ball is parallel with the valve body inlet and outlet. When the valve is shut, the ball is rotated so that the ball's hole is perpendicular to the inlet and outlet of the valve body and the flow is stopped.

Most ball valve actuators are of the quick-acting type, which require a 90° turn of the valve handle or stem to operate the valve. Other ball valve actuators are planetary gear-operated manual,  electrically operated motors, or pneumatic piston type. All actuators provide the necessary operating force to open and close valves.
Figure 1 



Ball Valve Advantages

A ball valve is often the least expensive of any industrial valve configuration and has low maintenance costs. In addition to quick, quarter turn on-off operation, ball valves are compact, require no lubrication, and give tight sealing with low torque.

Ball Valve  Disadvantages

Conventional industrial ball valves have relatively poor throttling characteristics (except when using a characterized ball, as shown above). A standard ball valve when in throttling position will fail because of because of the impingement of high velocity flow and the erosive effect on the partially exposed seat.

Ball Valve Port Patterns

Ball valves are available in the venturi, reduced, and full port pattern. The full port pattern has a ball with a bore equal to the inside diameter of the pipe.

Ball Valve Materials

Balls are usually metallic in metallic bodies with trim (seats) produced from "soft" seats referring to the elastomeric materials used such as PTFE (100% Virgin Polytetrafluoroethylene), RTFE (Reinforced Teflon®), TFM, CTFE, Polychlorotrifluoroethene, Polyether Ether Ketone, and UHMWPE. Care must be used in the selection of the seat material to ensure that it is compatible with the materials being handled by the valve.Ball valve bodies may also be made of various plastic materials for corrosive applications.

Ball Valve Stem Design

The stem in a ball valve is not fastened to the ball. It normally has a rectangular portion at the ball end which fits into a slot cut into the ball. The enlargement permits rotation of the ball as the stem is turned.

Ball Valve Bonnet Design

A bonnet cap fastens to the body, which holds the stem assembly and ball in place. Adjustment of the bonnet cap permits compression of the packing, which supplies the stem seal. Packing for ball valve stems is usually in the configuration of die-formed packing rings normally of TFE, TFE-filled, or TFE-impregnated material. Some ball valve stems are sealed by means of O-rings rather than packing.

Ball Valve Position

Some ball valves are equipped with stops that permit only 90° rotation. Others do not have stops and may be rotated 360°. With or without stops, a 90° rotation is all that is required for closing or opening a ball valve.

The handle indicates valve ball position. When the handle lies along the axis of the valve, the valve is open. When the handle lies 90° across the axis of the valve, the valve is closed. Some ball valve stems have a groove cut in the top face of the stem that shows the flowpath through the ball. Observation of the groove position indicates the position of the port through the ball. This feature is particularly advantageous on multiport ball valves.

For more infomration about industrial ball valves, contact Mead O'Brien by calling (800) 892-2769 or visit their website at https://meadobrien.com.

Monday, December 14, 2015

Valves Designed for Severe Service. Not Just Heavy Duty

severe service control valve
High performance butterfly
valve (Jamesbury)
From time to time, industrial process control applications involve very stringent and challenging performance requirements for the valves, process piping, and instruments that are part of the control loop. Control valves are a significant example where the impact of extreme fluid conditions require careful design and selection consideration to assure proper performance and safety levels are maintained in a predictable way.

Severe service is a term that describes valves used in application at the extremes of pressure, temperature, cycling, and material compatibility. While there are plenty of published and accepted standards for industrial valves, one does not exist to precisely define a severe service valve.


So, what then defines the selection of severe service valves, as opposed to general purpose valves?

There are a number of basic selection criteria that might point you in that direction, but in general they are:
  • Very extreme media or environmental temperature
  • High pressure drop operation that may cause cavitation
  • Rapid and extreme changes to inlet pressure
  • Certain types or amounts of solids contained in the fluid
  • Highly corrosive, or erosive process media.
Certainly, any of these criteria might be found in an application serviceable by a general purpose valve, but their presence should be an indicator that a more involved assessment of the fluid conditions and commensurate valve requirements is needed. The key element for a specifier is to recognize when conditions are apparent that might exceed the capabilities of a general purpose valve, leading to premature failure in control performance or catastrophic failure that produces an unsafe condition. Once the possibility of a severe service condition is identified, a careful analysis of the possible operating conditions will reveal the performance requirements for the valve.

When in doubt, its critical to discuss your special requirements with an experienced product application specialist. They have access to technical resources that can help with selecting the right valve components to meet your severe service applications.

For more information contact:

Mead O'Brien
(800) 892-2769