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• # Pressure tank drain time

Discussion in 'Calculations' started by sarathi, May 6, 2016.

1. ### sarathiNew Member

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Oct 2014
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Hi

I need to calculate the drain time of air pressured water tank (Ex. Sprayer) through a check valve and filter. The inputs are

1)desired flow rate is 5 kg/hr.
2)air pressure inlet for the tank is 9 bar.
3)Volume of Tank is 2 liters.

Please let me know, how can we make assumptions and proceed forward in this regard.

2.
3. ### CPPMableWell-Known Member

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Nov 2012
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Flow rate will be a function of pressure. As the pressure drops so will the flow rate.

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5. ### sarathiNew Member

Joined:
Oct 2014
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Hi

Thanks for your valuable suggestion. I've already gone through that forum. I forgot to tell that, my tank is in rectangular shape. And I've to use either pressure or Flowrate as an input. Where as in that forum, they have discussed about flow through channels. From one of thst discussion, they used Darcy weisbach equation. Though its well suited for pipes. But our case is different.

So, if we take flow rate as an input, what are the things needs to be considered? If you came to know about any formula in this regard, please share.

Thanks again!!

6. ### Darshak ParikhMember

Joined:
Jun 2016
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.Hi sarathi,

Since it is a pressurized chamber, flow rate can be calculated as follows.
Q(flow rate) = A(area) * Velocity.
As per Torricelli's law, v= (2*g*H)^0.5.
Since the air pressure is at 9bar, and will remain constant throughout the process, total pressure at the outlet side will be 9bar+(pressue due to liquid head).Pressure due to liquid head is constantly decreasing,lets say from initial h to 0 and hence you can safely assume pressure due to liquid head is (h/2) through the process.

Now,
Average flow rate= A*v.

Drain time= (total volume/avg_flow_rate)

Cheers.

7. ### sarathiNew Member

Joined:
Oct 2014
Posts:
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