Relief Valve for High Viscosity liquid 1

[Bill3752]

I am trying to find a RV to handle higher viscosity fluids. The highest case is 850 cp. I have run into a problem, as it appears that 160 cp may be the max that will work with conventional Dresser and Crosby valves.
Q1: You know of any reclosing certified RVs that will work at this viscosity?

I am looking at using at a Fulflo valve, but these are not ASME certified.
Q2: You know of anything similar that would be certified?

Depending on your input, I may look at a rupture disk, or a rupture disc and Fulflo (set below the RD) combination.

Thanks in advance.

 

[RVAmeche]

Based off the high cP I'd recommend a rupture disk without any other information. You should probably have a local catch tank or something for the RD to relieve into instead of a long piping run since the fluid is so viscous.

Alternatively, is it possible to heat trace the line or something to bring the viscosity down?

 

[Latexman]

Is the fluid Newtonian or non-Newtonian? If non-Newtonian, is it shear thinning? Maybe you'll get some relief because of that. Pun intended!

Good luck,
Latexman

Engineers helping Engineers

 

[Bill3752]

Latexman, actually I have a couple of cases. The highest viscosity case (850 cp) is Newtonian. Another case involves a thixotropic fluid - we have calculated the viscosity to be 430 cp at relief conditions through an appropriately sized RV.

Thanks, Bill

 

[georgeverghese]

If these are meant to work as thermal relief valves, then I wouldnt bother with sensitivity to high viscosity - I have specified spring loaded RVs' in TRV service similar service (hot bitumen), since the relief flow is very small.

 

[gguliye]

Sir,
I have included 850 CP into PRV2Size and it seems program can suggest me the different valves. Could u please recheck?

 

[Latexman]

How did you arrive at "160 cp may be the max that will work with conventional Dresser and Crosby valves"?

Good luck,
Latexman

Engineers helping Engineers

 

[don1980]

Note that you're talking about a fluid that has a viscosity that's approximately that of motor oil. 850 cp sounds high but it really isn't, relative to many other fluids like polymer melts or polymer solutions. A PSV will work fine in your application. The only thing that's different here is that the fluid won't flow as freely as water, but it will still flow just fine. At that viscosity it'll almost certainly be laminar flow, so calculate the pressure drop accordingly.

The fluids that are really problematic are those that are non-Newtonian, because they don't have a fixed viscosity value. You don't have that issue, which means your flow rate and pressure drop can be reliably calculated. Thus the PSV can be reliably sized.

 

[Hari Mech]

Hi Bill,

Crosby valves can work beyond 850 cP.

Viscosity has a relation with Capacity Correction Factor. (Kv)
When a liquid relief valve is required to flow a viscous fluid there may be the occasion to adjust the required orifice area for a laminar flow regime. If REYNOLDS Number is less than 100,000 then there will be a viscosity correction factor.

Valve selection wont be available only if If Kv is less than 0.3

 

[The Obturator]

The Viscosity Correction Factor "Kv" is not the preserve of Crosby Valve, it is from API-520 Part 1 (2014) Figute 37 (extract attached), and then from a concept originally developed in 1851 (more here

https://en.wikipedia.org/wiki/Reynolds_number

). But enough lecturing and back to PRV's, RV's and SRV's.....in ISO speak only the term Safety Valve is used.

In essence, a Kv less than 1.0 calculates a larger required orifice area to compensate for high viscous fluid. Sometimes dependant on the various incidental factors, you would end up selecting the next standard letter orifice up. In such cases you need to redo the Kv calculation with the new (larger) selected orifice area. You know when you have a viscosity problem when the revised larger calculated area using the new Kv, pushes your orifice size up again to the next standard size every time. That's then beyond the equations proper function.

For all suspect high viscosity fluids and/or a calculated factors of KV = 0.3 or less, talk to the PRV manufacturer for options including heating jacket, heat tracing or even heated nozzle. The idea being that the fluid is liquid enough at point of initial opening. A purge connection (eg. steam) is sometimes opted for on the valve body nozzle seat height, to "wash" the seating area after opening. The best SRV design here can be one with a "Flush Seat". This is where the actual vessel forms the bottom seat (nozzle) and the topworks of the SRV (disc) is in contact with the vessel seat direct. The advantage here is of course is less travel and obstruction of fluid to open the SRV cleanly.

Needless to say, pilot operated safety relief valves are a no no - heat (on O Rings). small piping/passages etc., but again, the manufacturer may have a solution - chemical barrier in the sensing. How about a spring operated valve with actuator to ensure opening? or even a rupture pin device/valve?

It is all dependant on the application etc. Sorry about the sermon but some time free here on a Friday afternoon.



Per ISO, only the term Safety Valve is used regardless of application or design.