Hi Paul
Having extreme difficulty accepting the description below about ball valves. It reads like an advert and is quite misleading. I hope you didn't do a cut and paste before agreeing with what your were posting. With quite a number of significant exceptions, ball valves offer significant engineering challenges when pressed into control service. Seat/ball wear, cavitation issues and contollability all require special attention. As for the claimed 10% of CV dead zone on "globe" valves, well, check out your own plant in the critical service areas; I hope you are doing better than 10%.
Cheers
Steve
-----Original Message-----
From: Paul Bowers [mailto:pbowers@pipingdesign.com]
Sent: Wednesday, February 02, 2005 12:55 PM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] New Current Interesting Links - Corrosion, Ball
Valves, Temperature Measurement
Click through to the pages mentioned below via www.pipingdesign.com's "Current Interesting Links" feature at the main page (these links are also archived at http://www.pipingdesign.com for future reference):
Temperature Measurement http://www.pipingdesign.com/transmitters.html
<<Temperature control is important for separation and reaction
processes, and temperature must be maintained within limits to ensure
safe and reliable operation of process equipment. Temperature can be
measured by many methods; several of the more common are described in
this subsection. You should understand the strengths and limitations of
each sensor, so that you can select the best sensor for each
application. In nearly all cases, the temperature sensor is protected
from the process materials to prevent interference with proper sensing
and to eliminate damage to the sensor. Thus, some physically strong,
chemically resistant barrier exists between the process and sensor;
often, this barrier is termed a sheath or thermowell, especially for
thermocouple sensors. An additional advantage of such a barrier is the
ability to remove, replace, and calibrate the sensor without disrupting
the process operation.>>
Flow Control With Ball Valves
http://www.pipingdesign.com/controlvalves.html
<<When a globe valve starts to open, it will always jump open rather
than move smoothly. In order to overcome linkage and internal
resistance, more movement is needed by the actuator than low flow
requires. Globe valves are installed with flow tending to push open the
seat. As soon as flow is established, the pressure pushes on the seat,
the stem rises, and more flow than needed occurs. There is a travel zone
where about 10% of CV rating occurs on opening. Ball valves do not have this jump effect. Rotation is slow, rack and pinion linkage is used, the
tendency of flow is to close a ball, and a high seal resistance, all contribute to smooth rotation without jumps, resulting in turndown ratios from 160:1 to 400:1, depending on quality of actuators, valves, and signal. Minimum flow is fully controllable under part load conditions. Ball valves with Belimo actuators are exceptionally good at control, and fully utilize the control signal.>>
Piping System Corrosion Control
http://www.pipingdesign.com/materials.html
<<Among other factors, the integrity and life of a piping system is
dependent upon corrosion control. As discussed in previous chapters of
this manual, internal corrosion of piping systems is controlled by the
selection of appropriate materials of construction, wall thickness,
linings and by the addition of treatment chemicals. External corrosion
can also be addressed through materials of construction. However, other
methods may be required when metallic piping systems are applied.>>
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Yahoo! Groups Links Received on Mon Feb 07 04:12:00 2005
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