Suggestions on pressure reducing valve sizing

[Purg]

Project info

7 story hotel with commercial kitchen and restrooms, 2 commercial water softeners, pool and hot tub with auto-fill.
2– 750,000 gal water supply tanks @ app 9500’ without any pressure regulation or reduction supplying the building through a 12” main reduced to 8” and finally 3” after entering the building.
water temp- 40f
water hardness- approx 50gpg or 855ppm
building elevation- 8500’
incoming pressure- 250psi
final outgoing pressure- 80
min flow- 1gpm
max flow- 250gpm

Flows are very intermittent but when "busy" the majority of flows are between 10 and 50gpm, mostly flush valves and faucets
looking to accomplish supply using a two stage reducing system as single stage has failed in the past due to the pressure drop. We currently have one 2" and one 3" line in parallel at the first station and a 1", 1 1/2" and 3" line in parallel at the second station. There is a 3" pilot operated globe valve (model 90-01)at the first station and the 2" line is currently only a service bypass. The second station has a 1" pilot operated globe valve (90-01)on the 1" line and a 2" reduced port pilot operated globe valve (model 690-01)on the 3" line while the 1 1/2 line has been isolated due to valve failure.

I've been working with Cla-Val for the past five years to come up with a working supply system for this building but after 3 failed recommendations and having to rely on the the regional branch they have me looking towards other manufacturers. Their latest recommendation suggests replacing our failed 3" lead valve with another 3" pilot operated globe valve, this time with a 3/4" direct acting low flow bypass valve installed on the main valve body (model 90-48KO). The 2" line would remain unused and all flows to the second station would go through the 3" - 3/4" valve. The second station would be a combination of direct acting valves on the 1" and 1 1/2" lines (model CRD-L) while the 3" line would keep the current 2" reduced port pilot operated globe valve (690-01).

My concern is that while the 3/4" bypass is supposed to handle up to 30gpm at 31-50gpm the disc in the lead globe valve will be hovering over the seat to maintain the low flows which in my opinion is what destroyed the previous valve trim and body. I'm also unsure if the lead globe valve will open and close fast enough to meet the demand of the second station without starving or surge issues. I've been unable to get other engineers independent opinions and instead they only recommend the manufacturers recommendation supplied by the regional branch because "it's from the manufacturer". The regional branch however can't and won't provide the details/specs they based their recommendation on so needless to say I am hesitant to go along with another one of their recommendation. Any opinions or suggestions would be much appreciated.

Pictures are of the seat and body from the lead 3" valve that failed.[/u]

 

[gerhardl]

Visual traces on the metal parts indicates cavitation, with typical uneven faces. This will only be caused by too rapidly flowing water, (e.g) small openings, too large pressure reduction and amount of water.

This will again confirm your suspicions that the equipment type is either mismatched for the actual (real) user pattern over time, or wrongly selected.

I have not studied amounts and user patterns, but there is a possibility that longer periodes (for instance night) might give a lower opening than the valves are constructed for.

A measurement over time or calculation per valve of flow can indicate if the flow is to low over periodes longer than recommended. Dimensioning figures originally given might not be correct for all situations.

Other valve-solutions might be far better for long-term operation with valves more adapted for wider ranges.


Good luck!

 

[HitokiriAoshi]

don't open a globe valve in less than 20% opening. consider changing plug shape, and do away with needle guide and find a body guide. use a larger valve in Y pattern and more streamline disc if necessary to achieve above. or pony up for a nice control valve.

 

[Purg]

Thanks for the replies, any manufacturer suggestions? The current manufacturer has proven to be very difficult to make it through their sales staff and speak with their engineering team.

 

[RVAmeche]

Cashco is cheap and has a wide range of products. Emerson has a ton of different regulators and my local rep is very responsive and helpful.