High Inlet Line Loss In PSV

[confusedchamp]

Stuck at dead end for high inlet line pressure loss.

The relief valve is located downstream of a pressure regulator. The regulator failure is the governing case and API orifice D is what is required for this case.

Now problem is the downstream line size of regulator is 1/4". Considering the standard inlet outlet size of PSV, I need a 3/4" line. Now in calculating the inlet line losses, i have considered the following,



[ul]
[li]Expansion loss from 1/4" line to 1.5" inlet line[/li]
[li]1.5" line loss[/li]
[li]1.5" line to to 3/4" contraction loss to PSV inlet.[/li]
[/ul]



No matter how much i change the inlet line size, the expansion loss from 1/4" to x" is dominating the pressure drop, and is coming more then 3%. (way beyond 3% upto 20%).

i am calculating the line loss for rated flow.

Any help to solve this is highly appreciated.

 

[SNORGY]

What is the regulator pressure involved?

If low enough, consider a regulator with integral relief. If that is feasible, the downstream PSV can disappear entirely.

 

[LittleInch]

Can't get my head around how normal flow is ok in 1/4" line, but you somehow need a 3/4" psv inlet. Where does this 1.5" line come into it? Your losses sound right, but can you post sketch of setup and explain why you can't use a psv with the same line size.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Latexman]

Sounds like the regulator is too big for the application. FWO flow must be quite excessive compared to "normal".

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529

 

[don1980]

Your options are to: (1) engineer a relief design for the current system, or (2) change the current system so that other relief design options are available.

1: For the existing system, a pilot operated PSV (POSV) might be the only solution. A modulating POSV allows you to calculate the inlet losses using the required flowrate, rather than the rated capacity of the valve. Alternatively, you can solve the problem by using a remote sensing POSV. Locating the pressure sensor upstream of the fittings that are causing the pressure drop.

2: Change the system to make the relief design requirements easier to meet. For example, change the regulator as Latexman suggested. Or, lower the pressure on the upstream side of the existing regulator. Possibly you could add a restriction orifice to limit the peak flowrate during a regulator failure.

Be creative in evaluating options. When you find that you don't have any good options because you're in a tight box, then consider redesigning the box to give you more room. The best option is the one that reliably solves the problem at the lowest cost.

 

[confusedchamp]

Thanks all for the timely advice.
Well i posted the same in other blog and got some leads about the problem.

The PSV selected orifice size is D with area 0.11 sq. in.
Now i was trying to take 1/4in line to 3/4" line in calculating pressure loss. As per API and ASME, the inside dia of all the fitting and line shall have same or higher then of orifice. Hence whatever line size i was selecting, always pressure loss was high.

The main problem is 1/4" line downstream of regulator. I have asked the same to system designer and awaiting response. It seems that the outlet line of the regulator cannot be made 1/4". Will post the developments.
Thanks all.

 

[MikeClay]

If you can maintain the regulator inlet piping pressure spec on the 1/4" outlet segment and then transition to the final piping design pressure at the 1.5 inch line, then the pressure losses in the 1/4 inch section would not be included in the inlet pressure loss calculation.

--Mike--

 

[hacksaw]

don't confuse the traditional "relief capacity" of a self contained regulator having a discharge pressure of 0 psig, with the failed open capacity of the same regulator with the relief valve at its rated accumulation.