# Calculating drop in gas pressure

• Cardigan9
Lower flow causes less friction and less pressure loss.In summary, Poles Formula can be used to calculate pressure drop in a pipe by using the flow rate, pipe diameter, length of pipe, and specific gravity of the gas. However, it is important to note that decreasing the flow rate will result in a lower pressure drop, while increasing the flow rate will result in a higher pressure drop due to the effects of friction.
Cardigan9
Poles Formula (see page 10 of attachment)

www.mech.hku.hk/bse/MEBS6000/mebs6000_1011_04_steam.pdf

Where have I gone wrong?

• q = flow (m3/h)
• d = diameter of pipe (mm)
• h = pressure drop (mbar)
• l = length of pipe (m)
• s = specific gravity of gas (density of gas / density of air)

h = ( q^2 * s * l ) / ( 0.0071^2 * d^5 )

q = 6 m3/h
d = 20mm
l = 19M
s = 0.58

The result is 2.459 i.e. the pressure drops by 2.2459 mb, which on the face of it looks fine, the problem is that if I reduce the flow rate the loss of pressure over the length of the pipe drops. Which in theory means that if I start with 21mb gas pressure and have a lower flow rate I end up with a higher pressure at the end of the pipe; that can't be right can it?

Last edited by a moderator:
Yes, that is correct. Higher flow causes more friction and more pressure loss.

## What is the formula for calculating drop in gas pressure?

The formula for calculating drop in gas pressure is: ΔP = (P1 - P2) / P1 x 100, where ΔP is the change in pressure, P1 is the initial pressure, and P2 is the final pressure.

## What is the unit of measurement for gas pressure?

The unit of measurement for gas pressure is typically expressed in Pascals (Pa) or kilopascals (kPa). Other common units include atmospheres (atm), pounds per square inch (psi), and millimeters of mercury (mmHg).

## How does temperature affect gas pressure?

According to the ideal gas law, as temperature increases, gas molecules gain more kinetic energy and move faster, resulting in an increase in pressure. On the other hand, a decrease in temperature causes the gas molecules to slow down, leading to a decrease in pressure.

## What factors can cause a drop in gas pressure?

A drop in gas pressure can be caused by a variety of factors, including leaks in the gas system, a decrease in temperature, a decrease in gas supply, or an increase in gas demand. It can also be affected by the type of gas and the type of container used.

## How can I prevent a drop in gas pressure?

To prevent a drop in gas pressure, it is important to regularly check for leaks in the gas system and repair them promptly. Maintaining proper gas supply and monitoring gas demand can also help prevent significant drops in pressure. Additionally, using appropriate gas containers and following safety guidelines can help prevent unexpected pressure drops.

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