Some clearance space is required otherwise piston hits on the cylinder head as it travels. Also expansion of piston occurs as it travels and very little clearance may cause the same problem. Also increased clearance space reduces compressor efficiency and increases its running hours.
So clearance volume must be kept around a reasonable value as instructed by the manufacturer.
Pasteurization requires that the milk is in custody for a specified time. The appropriate length for the holding tube can be calculated by the flow rate (Q) of milk and the diameter (D) of the holding tube using the formula: Length of holding tube, L = Q x holding time/A x η A = Area = pi/4 x sqr D Where an efficiency factor, η, of 0.85 is used in the model.