Reduced bore and full bore ball valve

[swemin]

I found two type of one side down (18"x16")and two size down (eg 18"x14") for reduced bore size for ball valve. What is the consequence in views of velocity, flow, etc. between two size down and one size down. What is the interanal diameter difference between them?

 

[zdas04]

A client recently asked me to price a 10-inch full port and reduced port valve for an application and was amazed to find that for that day the full port was less expensive. The only reasonable justification that I've ever heard for using reduced port valves is cost savings. Today those cost savings seem to be slim to none.

From a fluid mechanics viewpoint, the beta ratios are 0.88 and 0.78 respectively. API 14.3 has formulas for calculating permanant pressure drop across a restriction and using those beta ratios you get a number vanishinly close to zero permanant pressure drop. From a fluid mechanics viewpoint either one will give you about the same results as a full-port valve (within the accuracy of any calculations you can do on it).

From a mechanical-perations viepoint there is a huge difference. I saw a presentation once by the head of Tenneco pipeline group and he showed a 36-inch valve at the start of the line going under the river into Manhattan. He said that they pig that line weekly and it takes the pig between 2-5 hours to traverse each of the reduced port valves and he is often very concerned that pressures on the island will drop to dangerous levels before the pig clears the second reduced port valve. The big EPNG explosion in New Mexico a few years ago was due to corrosion that hadn't been identified because the line had to be exempted from their smart-pigging schedule because of the reduced-port ball valves every 5 miles.

I never buy reduced-port valves larger than 2-inch. I always specify full-port trunnion ball valves for anything bigger than 3 inch, any size valve on lines with less than 15 psi normal operating pressure (except drilled tank valves), or any size valve on a line with a normal operating pressure more than 300 psi. I've never had occasion to regret that decision.



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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