pressure reduction

[sweetfood]

I want to get other people's opinion on this matter. Pump is pumping fluid at 150 psig discharge pressure and at 350 gpm. I will be intalling metal tubing (1/4") on 1" existing connection to send sample to online analyzer. We also want to add manual sample line for analyzer check. Peole are concerned about possible high pressure when techs opens a valve to take manual samples since it is hazardous chemical. Tubing will be ~ 30 ft long total and returned to suction of pump. It is continous flow through tube. My quick calc indicates there will be plenty of pressure drop through 1" tee and 1/4" tubing by the time it gets to the point people want to take samples. Installation of RO has been suggested to insure enough pressure drop. That seems to make people's feel better...rather than getting pressure drop through a long tubing. Will it be better to install RO to insure enough pressure drop for manual sampling?? Pressure regulator has been also mentioned....

 

[BigInch]

NO NO NO. The transient analysis is what matters here.

When you first open the valve or an orifice, it would be at full pressure. When the line is static, there is NO pressure drop. Pressure won't drop until all the fluid in the tubing is moving. There can be a considerable acceleration of fluid near the end of the tubing as you open that valve, as basically that just depends on F = m * a

Forget the orifice plate. A finely controllable needle valve should be used, perhaps with a pressure regulator too. A pressure regulator will not let full pressure reach the valve, unless it is leaking across the seats when it is closed, also a possibility, in which case backup block valve and a blow off (junction located before the outlet valve) routed to a safe place may be necessary. How you want to handle that exactly depends on the toxicity of the fluid you're dealing with.





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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[sweetfood]

Thanks for your input. It is diluted chemical stream. Chemical concentration is less than 5% and the rest of it is water. Although it is diluted, it could cause some minor safety issue on people. For this reason, RO can be used instead of pressure regulator?

 

[BigInch]

Not in my book. Not knowing the chemical, I will defer to the other people's consideration that it is dangerous enough to warrant concern about this issue.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rneill]

Use a manual needle valve and if you are concerned, buy one that is designed for precise flow control.

I've never seen anything other than a manual needle valve on a sampling system. If you just crack the valve, you will have only a very small amount of flow as there will be a large drop across the valve.

The valve manufacturers provide charts of the Cv vs. number of turns so you can find one appropriate to your system.

For a relatively high flow valve, you might consider a Swagelok N Series (Ball Tip Stem) or Parker U Series valve. For a low flow valve you might consider an Autoclave Engineers 10V Series valve.

 

[rmw]

Let me get this straight. Your sample loop begins at the pump discharge and ends at the pump suction and acts as a continuous recirculation loop, right? That is what I understood in the OP. Does your sample point tee off of that loop? That is how it seemed to be described to me.

If so, what is the pressure at the pump suction? Where along the loop do you want to put the sample point?

Notwithstanding that, the recommendations for needle valves are good advice, or use a sampling valve designed specifically for sample taking. Check this site for 'process valves.'

http://www.strahmanvalves.com/

rmw

 

[sweetfood]

You have desribed it correctly. Pressure at suction is based on the liquid level in storage tank and I would say it is ~ 20 psig. Sample line would come off discharge of pump which is pumping at 150 psig. Sample would go to online sensor/analyzer and then back to the suction side of pump. On the return line from sensor/analyzer, line would tee off to go to manual "sample chamber" where techs can take sample manually to check sensor/analyzer performance. There is nothing special about this "sample chamber". It was made by the plant people to take sample and drain properly. Drain line is connected to the designated plant chemical drainage. They just open a valve and take samples. This chamber is connected to suction side of pump where pressure is much less than discharge for safety reason. They want to use the same chamber along with a new automated analyzer system.