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Clogging of Relief Valve Inlet Spool

Clogging of Relief Valve Inlet Spool

Clogging of Relief Valve Inlet Spool

Hello all,

I have a pressure filter vessel with a PSV mounted on a 7" long spool from the vessel. As the vessel is a filter, solids-rich liquid (especially filter-aid) gets trapped in the spool and over time, the spool gets clogged with solids to the point that valve operation is compromised.

A few options that I have considered still are not satisfactory:

1. Install a bursting disc before the PSV - the spool will still get clogged amd affect pressure protection.
2. Reduce the spool - this will be a modification to the pressure vessel and will require new drawings and hydraulic testing (expensive).
3. Top hat bursting disc design - this allows the disc to be flush with vessel contents allowing it to be frequently cleaned by the vessel contents. It is the most viable solution so far but is far too costly (around £2,500 per bursting disc as it's a bespoke design).

There has to be better solutions.

I would very much appreciate your ideas.

Thank you.

RE: Clogging of Relief Valve Inlet Spool

Can you back-purge the inlet line with anything? Clean process material? Nitrogen?


RE: Clogging of Relief Valve Inlet Spool

Maybe move the PSV to the filter outlet?

RE: Clogging of Relief Valve Inlet Spool

If you do not have 'Pad' type nozzles I do not know what to suggest. Sorry.

If the vessel PSV nozzle is a 'Pad' type connection then you should put a Rupture Disc directly on the vessel nozzle (under the 7" spool piece). This would reduce the amount of cavity available to plug-up ahead of the PSV.

Sometimes its possible to do all the right things and still get bad results

RE: Clogging of Relief Valve Inlet Spool

Moving the PSV to the outlet would most likely result in the PSV being exposed to the lowest pressure in the vessel and might not protect the vessel if the filter plates are blocked. Moving the PSV to where perfomance isn't affected is one of the options I'm looking into though.

Flushing the spool routinely is a viable option, however it will rely on operator diligence if manual, an automatic valve on a timer is possible but might open at the wrong time. I'll consider this in a bit more.

I'm not familiar with Pad nozzles so I doubt we have it. Web search isn't giving me much either but I'm curious, will you provide a bit more info please?

Thank you all, please keep the ideas coming.


RE: Clogging of Relief Valve Inlet Spool

I guess there has been a change in terminology from when I last used a 'Pad' type Flange. Now they are called Studding Outlets.
Look here:

However you would need to foresee the need and install one of these when you build the tank. It is not a simple add-on after-the-fact.

Sometimes its possible to do all the right things and still get bad results

RE: Clogging of Relief Valve Inlet Spool


Fair enough; I don't have the vessel or system details in front of me, but from what little I understand, you will want to put the PSV into as "non-cruddy" a spot as you can, otherwise every time (if and when) it lifts it won't re-seat properly and it will cause other grief.

RE: Clogging of Relief Valve Inlet Spool

Find a way to install the PSV in such a way that the entire path from the vessel to the PSV inlet nozzle is free of horizontal sections and pockets. Solids cannot accumulate if solids can free-fall from the inlet line.

Process Engineer, MSChE

RE: Clogging of Relief Valve Inlet Spool

Agreed, the PSV inlet line should slope continously back to the pressure filter, so solids cannnot collect in this line - sounds like there are low point pockets in this line at the moment. Also, the PSV inlet line should be oriented as a top tap off the source-main line.

RE: Clogging of Relief Valve Inlet Spool

Thanks for that. The vessel in question does not have the studding outlets but something I'll bear in mind in future.

I consider re-seating as a valid problem so the valve needs to be inspected if it ever lifts.

EmmanuelTop & Georgeverghese,
The PSV is directly on a vertical spool. A bit of the filter-aid/product just sticks to the spool everytime and builds up overtime as the spool never experiences a flushing motion.

Thanks all.

RE: Clogging of Relief Valve Inlet Spool

For slurry PSV service we recommend a nitrogen/fuel gas/inert gas pilot operated PSV. Sometimes a large dome, low pressure drop, filter is placed over the inlet to the PSV to extend the life before shutdown.

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