4 replies to this topic

[Bladee]

I have a query regarding pressure relief capacities for package boilers. Recently we have installed two package boilers from different manufacturers.

Boiler 1 - 10 tph @ 9.5 barg is fitted with two SRVs with a combined relief capacity of 26.5 tph

Boiler 2 - 8 tph @ 20 barg is fitted with two SRVs but the combined relief capacity here is just 8.2 tph.

Can anyone help explain why these pressure relief capacities are so different? (Valves are all sited on the steam drum & they are both waterside package boilers. Both were manufactured within Europe)

Look forward to hearing any responses

[fallah]

Bladee,

With such limited information, it could just be mentioned that seems the SRV's set of boiler 1 is oversized.

Fallah

[Art Montemayor]

Bladee:

I also am of the opinion that, for some strange reason, Boiler #1 PSVs are oversized. This may yield an operating problem: the PSVs will "chatter" and may damage themselves in so doing.

However, there is another potential problem that I would be very concerned about: you should have received certified, checked, and signed Data Sheets for each of the safety valves (which should be filed in the engineering department) and these will probably be required by your insurance company in order to ensure that the boilers are properly protected. This is a major requirement when it comes to boiler operation in the USA or Europe. These same Data Sheets will reveal the controlling relief case for the PSVs as well as the selected size and orifice in accordance with the calculated relief capacity. Is your insurance company aware of the discrepancy in the PSV capacity? You certainly want to make sure that they are aware.

[Lowflo]

Since relief valve orifices come in discrete sizes, it's not uncommom to find that they have far more capacity than required by the system. It does appear that the vendor mistakenly selected bigger valves than necessary for Boiler-1, but I'm not ready to jump to that conclusion, or to say that these valves will chatter. There's no doubt that they'll cycle more frequently than the valves on Boiler-2, but that's all we can say with certainty.

[Bladee]

<sub>Many thanks for all the valuable information.

We do have certificates for all the valves concerned & the insurance authorities have copies.

I've tried to get my hands on some standards (EN 12952/12953) to see what they contain - but so far have been unable to secure any (for free!!). Certainly in both cases the valves will relieve the steam overpressure should it ever arise - but I am confused as to why boiler 1 is so oversized. Is it oversized because of information within a standard - or have we paid for something we just don't require? All very confusing.

If I'd been designing the systems - on boiler 1 I would downrate it & for some safety margin on boiler 2 I would increase it.

Fortunately for boiler 2 the site have installed an SRV on the steam main to the plant - so we are in the "safe" margin.</sub>

Edited by Bladee, 01 June 2012 - 05:36 AM.