These are the minimum and maximum speeds the compressor will actually run. It is not necessarily the rated speed of the compressor or engine. For fixed speed units, the minimum and maximum speed would be the same number.

This is the rated brake horsepower for the compressor or driver (whichever is less).

This is the diameter of the piston rod. It reduces the swept volume on the crank end of the piston.

A double acting cylinder may be operated single acting by either removing the head-end suction valves or by holding the suction valves open by using valve unloaders.

This is the actual inner diameter of the cylinder.

This is the nominal pipe size of the cylinder in inches. For example, if the rectangular nozzle was 7” by 14”, use a Cylinder Nozzle NPS of 8”. The cylinder nozzle size affects the recommend outer diameter of the pulsation bottle, but it does not affect the recommended volume of the pulsation bottle.

This is the temperature of the gas before it enters or leaves the cylinder.

This is the relative volume change of a gas in response to a pressure change. For an ideal gas, it would be 1. For a sweet natural gas, the compressibility on the suction side would range from 0.88 to 1.00 and on the discharge side would range from 0.86 to 0.98. It is dimensionless, therefore the numbers are the same in Imperial or SI units.

This is the heat capacity for the gas in a constant pressure process divided by the heat capacity for a gas in a constant temperature process. It is dimensionless, therefore the numbers are the same in Imperial or SI units.

This is the ratio of the mole weight of gas to the mole weight of dry air. For a sweet natural gas, the specific gravity would range from 0.56 to 0.7. It is dimensionless, therefore the numbers are the same in Imperial or SI units.

Compressor model	Distance between throws (in)
Ariel JG, JGA	24.00
Ariel JGC, JGD	45.00
Ariel JGH, JGE, JGK, JGT	42.00
Ariel JGR, JGJ	32.50
Ariel JGI, JGM, JGN, JGP, JGQ	0.00
Ariel KBB, KBV	55.00
Ariel KBU, KBZ	48.00
Cameron Superior MW6, SW6	36.00
Cameron Superior W7	48.00
Cameron Superior MH6 or WH6	44.00
Cameron Superior WG6 or WG7	48.00
Cameron RAM-54	36.00
Cameron CFA-34	24.00
Dresser-Rand A-VIP	35.38
Dresser-Rand B-VIP	38.00
Dresser-Rand C-VIP	38.00
Dresser-Rand D-VIP	45.00
Dresser-Rand HOS	45.00
Dresser-Rand BOS	55.00
GE Gemini E, ES, F, FS	47.00

Note: the above dimensions are provided for information only and should be verified before use.

The formulas can be found in section 7.9.3.2 of API standard 618, 5th edition. The formulas are:

• minimum suction surge volume =
  7 * (displaced volume per revolution) * (isentropic compression exponent * suction temperature / molar mass) ^ 0.25
• minimum discharge surge volume =
  1.6 * minimum suction surge volume / (stage pressure ratio) ^ (1 / isentropic compression exponent)

API 11P has been replaced by ISO 13631. ISO 13631 (and similarly for API 11P) calculates the minimum surge volume by multiplying the cylinder swept volume (of all cylinders connected to the surge volume) by a factor which is shown in the figure in Annex B.

If a compressor operates over a range of operating conditions, then the conditions which result in the largest bottles should be chosen. The table below assumes the cylinder bore sizes have been chosen.
 

Operating condition selection criteria to calculate large (worst case) bottle sizes
Technique	Suction Bottle	Discharge Bottle
API 618 5th Edition	- Lowest molar mass   (specific gravity) - Highest suction temperature	- Lowest molar mass   (specific gravity) - Highest suction temperature - Lowest pressure ratio
API 11P	- Highest pressure	- Highest pressure
Wood VDN	- Lowest molar mass   (specific gravity) - Highest suction temperature	- Lowest molar mass - Highest suction temperature