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Sizing vacuum pump

Sizing vacuum pump

(OP)
Good day,

I have a piece of lab equipment that measures gram per litre solids concentration in certain suspensions.

This is a network arrangement that has been recently upgrade to handle several additional samples. However, the existing vacuum pump has been rendered inadequate. I am in the process of sizing a new vacuum pumps for the applicationand am having trouble inquantifying the flow rate requires to create the vacuum.

The situation posed may be a bit vague but can anyone point me in the right direction?

RE: Sizing vacuum pump

Do you do it by filtration method? If so, how many samples you take at a time and what is the flask volume in each case? What filtration time you require?

Regards,

Eng-Tips.com : Solving your problems before you get them.

RE: Sizing vacuum pump

(OP)
Quark,

Yes, it is a Filtration process. 9 samples (avg) at a time are taken at a time with a flask volume of 1000ml.

Filtration requirement ideally would be 3 minutes based on the sample type.

RE: Sizing vacuum pump

OK. So the total volume is 9 x 1 liter = 9 Liters(0.318 cu.ft)

Generally for filtration we have to apply a vacuum level of 300mm of Hg gauge or 460 mm of Hg abs. at sea level (beyond this there will be problems of filter paper rupture)

Vacuum pump capacity can be calculated by

S = (V/t)ln(p1/p2)

Where S is vacuum pump capacity in ACFM
V = volume to be evacuated in cu.ft
t = time of evacuation in minutes
p1 = initial abs. pressure
p2 = final abs. pressure

So, S = (0.318/3)ln(760/460) = 0.106 x 0.502 = 0.053 ACFM.(i.e vacuum pump should have a capacity of 0.053 CFM at 300 mm of Hg gauge)

This is the ideal capacity of vacuum pump required.

You have to add atleast 10% for leaks, use actual barometric pressure at your place, use correct filtration pressure what you maintain and also include volumetric efficiency of the vacuum pump.

This calculation gives you a base for further treatment of the subject.

Here is the best paper I found, so far, about the vacuum systems. Download it for better understanding of the vacuum system design and for your future reference.

http://www.sterlingfluidsystems.com/art/procam/pdf/FundamentalsRev1.pdf

Regards,

Eng-Tips.com : Solving your problems before you get them.

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