I am trying to improve an air pump to an gymnastics airtrack regarding the pressure drop in the pipes. In general the system consists of a vacuum cleaner motor, some 2" pipes, valve, T's and flexible 2" PVC hoses with Camlock connectors.

Furthermore the Camlock connectors for the hose locally reduce the pipe size to about 1.6 inch in diameter and the connector itself is not ideal. Can I in some way estimate the pressure loss from such connectors? Or do someone already hold the right friction factors for such connectors?

It is difficult to pinpoint any error without seeing all your data, but it looks to me that you have made an error in calculating the 2700 Pa pressure drop in the orifice calculation. Apart from that it all looks reasonable (within your expected accuracy criteria).

I took your air flow of 25 m/s in a 50 mm ID pipe to give a flowrate of 175 m³/h. For air at 25C and atm press with a density of 1.2 kg/m³ and a viscosity of 0.023 cP I get a pressure drop of around 700 to 1000 Pa for a 3 m section of pipe (depending on the roughness and exact ID). This is close to what you have measured.

For a 1.6" orifice I get a permanent pressure drop of 450 Pa. Be careful in using the flowmeter formula for orifices because it will give you the pressure drop between the tapping points and not the permanent pressure drop. There is always some pressure recovery after the tapping point.

I would think that your approach of calculating the connectors as two changes in diameter would be better than taking it as a sharp orifice plate, but doing this I get a higher value than you did. But it depends on the actual air flow you used and you have not specified that.

If you give the actual ID of your pipe and the air flowrate you have used I can do a closer comparison with my calcs.

BTW, "inch wg" is inch water gauge. This is the height of the column of water if you measure the pressure with a manometer.

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