Position of the handle of the isolaton valve of the pressure safety valve (PSV)

Why is there an isolating valve that can be operated easily in the same line as one containing a pressure relief valve? What does the HazOp Study report say about this?

Never heard of placing an isolation valve in the same line as an pressure relief (safety) valve. Seems it would defeat the whole purpose of the safety valve.

Quite.

Ive spent many years on piping systems. I must admit that I am just not following this question. Please clarify? I am sometimes a bit more left brained, or right brained, or mid brained....oh never mind.

To my knowledge, the handle of the isolation valve (ball valve) is normally placed vertically in the direction of the flow. You should be able to see from a distance that the valve is in open position. These isolation valves should be locked open.

I would agree with other post ,that the ISV needs to be locked in the open position and be located up stream to provide for service to the PSV. The reason for the horizontal run is because of contamination ,water dirt etc.

Del

I have read all the replies in this post but I must admit most miss the point of an Isolation valve. It is correct that the handle should be in a position of easy viewing as if it was hidden, then its real purpose would be lost.

ISOLATION is primarily for 'OH&S' Occupational Health and Safety when maintenance work has to be performed on the system or in the event of a failure downstream from the isolation point. Secondarily, the Isolation point "Must Never Be Locked" in the 'OPEN' position as it could not be shut in any emergency.

PLEASE THINK SAFETY AT ALL TIMES!

OH&S Officer

TECMATE, I presume under "any emergency" you mean failure of the PRV. In case of a PRV failure, the process has to be shut down unless the PRV can be replaced in a very short time. The "locked open" isolation valve is regulated by OSHA PSM.
In cases where the process cannot be shutdown an installed spare PRV can be used.

Not in all cases you need to install an isolating valve downstream of safety valve. And, as a rule of thump, in piping system the handle arm of the valve must be located parallel to the pipe line when the valve is open, and perpendicular to the pipeline when the valve is closed.

Abdel is exactly correct here. Perhaps I'm thick headed but I am confused by the horizontal thing.

Piping systems go up, down, even at an angle. So the horizontal has me stumped.

But if the question is perpendicular vs parallel then the valve handle should, as stated, run parallel when open; whether the line is vertical, horizontal or angular.

As to the location of the valve being upstream or downstream of the PRV (pressure release valve; It can be either. Depends on the system. Typically there will be one US of the PRV that can be shut to prevent the system from continuing to build pressure.

Of course there are pressure loops, bypass loops expansion loops and others that can effect the valve configurations.

But always inline open.

cr3

For information purposes, the practice is the converse on piping systems relating to braking systems on the ends of rail vehicles. The reason is that a passing obstruction (a minced bird, perhaps?) that comes into contact with the valve handle at speed must not cause the valve handle to swing shut and in so doing isolate a part of the braking system of a train; to do so would be potentially a very serious compromise of the performance of the braking system. So, contrary to industrial practice, on rail vehicles' brakes, between vehicles, a handle perpendicular to the pipe means "valve open".

hi Dear this is waseem,According to my knowledge is concerned it is horizontal bcs horizontal position of valve show's that it is in open condition,and this is placed in the line of PSV therefor it shuold always be in the open condition to avoid any accident bcs of high pressure.

i am mechanical Engineer in Camphor and Allied & Products

pls reply after receiving this answer at hiwaseem786@yahoo.com

Things to consider in deciding the orientation of gate valves include ergonomics to allow ease of operation by the operators, the position of the gate guides in fouling service.

It is safety related. If for some reason the stem breaks, the gate will not slide down, cutting off the relief path. This is common practive for isolation valves in relief headers, the stem never points up, or even above the horizontal.

Hi All. Usually the type of valve used in this application is a gate valve, and there is a risk (albiet a small one) that the stem or connection to the disc could fail. If the valve stem is in the vertical or above horizontal position, then the disc could fall into the pipe line and block it off. It is common practice then that the stem be below the horizontal to prevent this. Of course, this is only applicable if the pipeline is running horizonally.

You did not give us some of the important information with which we would use to give a proper answer. So I will make the following assumption.

The valves are Gate Valves. Right?

The orientation you are talking about is the orientation of the "Stem" of the Gate valve not the hand wheel itself.

If so then my answer is:

"All Flare system Gate valves SHALL be installed so the Stem is in the horizontal position (never vertical)."

The reason for this is an age old fear that when in the vertical position the disc (of the gate valve) might come free from the stem and fall down to the closed position. If that happened then sure enough there would be a huge relief event and the flare would be blocked.

We all know that Gate valves are designed somewhat different today than they were 75 to 100 years ago and few if any would have this problem but the horizontal only practice persists.

This "Rule" does not effect the stem orientation of any other type of valve (i.e.: Ball, Plug, Orbit, etc.).

__________________

What if your PRV could see cryogenic liquid? in LNG service all extended bonnet valves should be installed with the bonnet upwards. Should we violate EN-1473? or the recommended practices of installing gate valves in PRVs in horizontal position, to avoid the gate drop?

Thanks

Are you talking about PRV as in pressure reducing valve or PRV as in pressure relief valve? If you are talking about a pressure reducing valve you would put the handle on the way the valve is made or if you have a choice as in certain ball valves it would be perpendicular with the pipe when in the off position. This is a rule of thumb that I have followed for the last 28 years of installing and maintaining piping systems. I have never heard of putting an isolation valve in a PRV (pressure relief valve) line. We have literally hundreds of PRV's (pressure relief valves) in the paper mill that I work in and I can attest that there is not one isolation valve in any of the lines. In the USA the National Board Inspection Code requires that there is a pressure relief devise on all vessels that have a pressure above 15 psi. and that there is no way of isolating the PRV while in service. Our insurance provider and our Authorized Inspector would not allow it. I must surely be missing something here because you are saying pressure safety valve and I can't imagine why you would want to have a way to isolate your safety valve.

pipewelder

I believe he is indicating that there is an isolation valve upstream followed by a PRV and then the pressurized unit/whatever.

The isolation valve US would be shut to prohibit a continuing pressure build DS while allowing the pressurized unit/whatever to relieve through PRV.

In Semiconductor fabrication facilities where we have literally thousands of gases and chems this configuration is allowable.

Then again I could be wrong. It has already happened once today. Of course that was while talking to the She - nothing technical of course.