Reducing Pressure/Throttling flow - Severe Application

[Overbudget]

I have a vertical turbine pump delivering 800 gpm @ 420 psi at the pump discharge. I want to divert some flow from that stream to spray nozzles to clean an intake screen. No other water supply is available. The screen needs 30 gpm at 40 psi. I was looking at adding a tap in the piping and using a globe valve or needle valve to reduce the pressure. To get that flow with that pressure loss, the required Cv works out to about 1.5. I can get a 1" Class 300, bronze globe valve that will produce that Cv in a partially closed position, for about $200. I could go to a 1/2" globe valve and get the Cv I need with the valve full open. The alternative would be stainless steel needle valves made out of bar stock with a similar Cv values. It looks like these go for about $50.

Even though the math and the Cv calculation comes out "right" it still seems like a lot of flow and a lot of loss to create for a relatively small and simple valve. Are either of these valves going to have a life expectency of more than about a week in that service? For the price, I can put two or three of these valves in series, and either take the pressure down in steps or do it all in one valve and switch to the second or third valve when the first one starts to lose effeciveness.

Can anyone offer any thoughts?

 

[LittleInch]

If you're going for real low value stuff, look at multiple orifice plates. Much cheaper.

You'll probably need three or four of them to avoid excessive velocity in any one of them, but are very cheap....

All depends on how accurate you want your system.

My motto: Learn something new every day

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

 

[MJCronin]

Since your desired pressure at the spray nozzle is steady, why not investigate one of those hardened "multiple orifice" devices ( or recirculation valve type devices) used on boiler feedwater recirculation piping ?

http://delta-p-online.com/2012/02/02/automatic-recirculation-valve/

http://cuservices.net/products_c500.html

Regards

Keep us in the loop....... let us know what your final choice might be.....

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[LittleInch]

Snap!

My motto: Learn something new every day

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

 

[Overbudget]

Thanks for the leads! I don't run into this stuff very often in municipal water and sewer projects, but now we're doing work for gas companies, and I don't have all the answers.

I didn't like the looks of the devices with multiple orifice plates in series, because it looks like cleaning it could be a pain.

I'm liking the looks of a Multi-Orifice valve, which is also called a choke. It has two discs with one or more holes that can be rotated relative to each other. It looks like it can be cleaned by rotating the discs. Probably should provide a downstream blowoff and valves to facilitate cleaning.

The manufacturer I'm looking at has a web site with pictures of an offshore drilling platform and a well head (so I know I'm in the right place, LOL), plus lots of data, and a nomograph showing that my application is right in their range. I'll call them tomorrow and get a selection and pricing.

I think that the flow/pressure can be manually set using a pressure gauge on the downstream side. The spray nozzles will have a characteristic curve, so if I know the pressure, I know the flow. It would be pressure that would damage the spray system anyway. Will also provide a strainer on the low pressure side to protect the spray nozzles.

Thanks, that helped a lot.

 

[LittleInch]

OK, I'm sure both of us would have suggested a choke valve, but you seemed to be looking for a low cost solution. I'd be interested to see what estimate of cost you get for a choke valve - great valves, the hardened trims will last a long time but not cheap....

If your supply is "dirty" then just add a filter with a mesh size smaller than your smallest orifice plate hole.

My motto: Learn something new every day

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

 

[Overbudget]

Yeah, it did look like I was going cheap, but I was actually looking at familiar things that happen to be cheap.

The Choke valves will be about $700 to $800 each which isn't bad in a project that will go well into seven figures. For this client it's all about reliability.

Thanks again. I needed a nudge out of my box.