OT: Fluid Dynamics for Idiots

I know we should use gate valves but according to the boss "we already bought these orifice plate unions and have put pipe marks on them so they can't be returned". In other words, in defiance of common sense, we are going to use the wrong tool for the job, but no one here wants to take responsibility for drilling them to the wrong size.

Now for two days they have been passing the question around trying to get someone to make a decision about what size holes to drill in these parts.

The goal is to get the flow into all three tanks (not shown) about the same rate.

I don't really know how to calculate this, so if someone can give some clues or wants a puzzle to solve I would appreciate the help.

EDIT: All dim units in inches.

Okiepc: I used to work for a steel pipe company, once we had a problem to raise three hydraulic cylinders at the same speed at the same time. Solution use a flow divider one input three outputs, if my memory is not betraying me the company name is delta hydraulics or similar.

Just use the biggist you can find they will most likley cuss you when your gone anyway l.o.l

widelto said:

Okiepc: I used to work for a steel pipe company, once we had a problem to raise three hydraulic cylinders at the same speed at the same time. Solution use a flow divider one input three outputs, if my memory is not betraying me the company name is delta hydraulics or similar.

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Appreciate the thought, but they won't even buy gate valves.

bce123 said:

Just use the biggist you can find they will most likley cuss you when your gone anyway l.o.l

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After my discussion with the director yesterday...yes, they are scrambling trying to figure out how to pacify me and keep me and all I really need is weekends off. Anything short of that, and well, their lack of planning does not constitute an emergency for me.

Okie

Why the need for equal flow to each tank?

I can see a need for near equal "percent full"

Could you overflow from tank A then to B who then overflows to C?

If you put all three on a common header then the level in the three should be close to equal not counting head from flow velocity. Sort of like what your drawing shows.

Said with chuckle "here we go again - need more of those nit picky basic design questions.

Gate valves are not best for flow control - globe is the preferred / optimum.

Dan Bentler

leitmotif said:

Okie

Why the need for equal flow to each tank?

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An attempt to minimize the disturbance to the solids in this waste water (this is what I was told).

Okay, so globe valves...

This is one of those deals where I am sure if it is anywhere near close to equal flow it will be good enough. I just thought it was an interesting puzzle, opportunity to learn something new, and wanted to help one of my techs get this aspect of the project behind him, since he's not getting clear advice from his superiors.

rationale for equal flows ?

Why is the flow rate important vs the fill level ?
What size are the orifices now ?
You have a 275 GPM pump and 3 inch piping = are the orifices bigger than 1 inch ?
A small orifice should give equal flow rates by loading the pump. The real trick is high flow volume and equal fill rates.

GlennA said:

Why is the flow rate important vs the fill level ?
What size are the orifices now ?
You have a 275 GPM pump and 3 inch piping = are the orifices bigger than 1 inch ?
A small orifice should give equal flow rates by loading the pump. The real trick is high flow volume and equal fill rates.

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Yes, I should state that I was handed a sketch of the dimensions and have not even seen these orifice plates. They were described to me as pipe unions with plates built in. And it was mentioned that we want minimal back pressure on the pump.

That this is incredibly stupid goes without saying. You can get a ball valve for around $100 apiece.

http://www.mcmaster.com/#ball-valves/=h2an4r

You can get them for less going to a local plumbing shop!

If the working fluid is wastewater you don't want either a globe or a gate - both will collect debris and experience wear from entrained solids. On this size an eccentric plug is best, but ball valves should do the trick. Because one side is free flow if you mount them on the end of the pipe plastic valves would probably be just fine and cheap.

Orifices won't necesarily guarantee equal flow off a common header, but if the pressure drop through them is high enough you could get close. The pressure drop difference through the fittings and velocity head changes will make identical orifices pass different flows in each location. However, the extra pressure drop through the orifices and resulting increase in pump power would pay for the valves in short order. Not to mention all the cost of screwing around!

To answer your question, flow through an orifice for water is found here: http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm for air

http://www.pumpcalcs.com/calculators/view/103/ for water.

http://www.ask.com/wiki/Orifice_plate for explanation

For a drilled hole use orifice constant C = 0.6
"Penny wise and pound foolish" as they used to say.

Make the following assumptions:

You want max flow so pump discharge pressure will be zero at start due to tanks being empty.
Disregard all piping up to the first tee as all three orifices see the headloss introduced here.
Orifice 1 sees no headloss.
Orifice 2 sees one tee plus 77' of pipe at 2/3 flowrate
Orifice 3 sees two tees plus 77' of pipe at 2/3 flowrate plus 84' of pipe at 1/3 flowrate.

Determine the total headloss for orifice 3. Adjust orifice sizes until all headlosses are equal.

Shawn

Thanks for the pointers, guys. I will try to use this info to get them close.

I am pretty sure that the fluid is warm water with mostly liquid animal fat entrained.

Most likely, after I spend an hour or two tomorrow trying to give them some sort of scientific answer I will find out they just w.a.g.'d it.

Yes, three of us suggested valves right away, but alas, the mentality here defies wisdom so often...

12 more days...

OkiePC said:

12 more days...

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Until vacation or a new job?

The Plc Kid said:

Until vacation or a new job?

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New job.

Animal fat and or bones and who knows what else? Definitely ball or maybe butterfly valves.

OkiePC said:

New job.

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Congrats!