Suction Line Sizing

[homerphish]

Is there a way to figure out exactly how much compressor BHP will rise if a suction line is under sized? Also, what is the maximum allowable pressure one could have in a suction line?

 

[imok2]

You must mean how much will BHP go down with an undersized suction line! The suction line should be no more then 2# PD or about 2 degrees. The best way to determine if a compressor is pumping properly is with a set of gages, an amp meter and the compressor specification sheet. Measure the operating discharge and suction pressure as well as the amperage. Using the compressor curve sheet,available from the manfg. compare the amperage reading at the measured pressures. Because of voltage variations and measurement inaccuracies the measured amperage should compare to the actual curve sheet values within +/- 15%. Never check compressor operation by closing the suction valve to see how low the suction will go. This might actually cause damage to the compressor because of heat build up.

 

[25362]

The piston rod in reciprocating compressors can fail if overstressed. If the suction pressure goes down the [Δ]P between discharge and suction acting on either side of the piston times the area of the piston results in forces that may break the piston rod.

The compressor manufacturer has indeed calculated the temperature rise for the maximum [Δ]P to which the piston would be exposed.

Since a higher [Δ]P results in a higher discharge temperature, monitoring it serves to activate a high-discharge temperature trip to prevent overstressing the piston rod.

It is sometimes worth repeating that the high-temperature trip is not meant to protect mechanical components from wear and tear due to high temperatures, but to protect the machine from the consequences of a piston-rod failure.

 

[ClydeMule]

What kind of compressor? Size?