STANDARD TERMINOLOGY

In order to make communications between the people involved with HASKEL boosters less confusing, a "standard" parts description is needed. Part numbers and model numbers are adequate for system assemblies, but the individual areas of the booster involved in trouble-shooting need "generic" descriptions applicable to all models in order to simplify the task of communication. The following descriptive names are recommended to facilitate transfer of information on booster problems.

AIR DRIVE

The low pressure air driven section of the booster which moves the air drive piston alternately in opposite directions to power the gas section for generation of flow and pressure.

CYCLE

One complete back and forth motion of the air drive piston. There are two strokes to a cycle.

STROKE

The travel of the air drive piston from one end cap to the opposite end cap. A stroke is one-half of a cycle.

VALVE END CAP

The air drive end cap containing the cycling valve and the pilot fill valve.

PILOT VENT END CAP

The air drive end cap (opposite to the valve end cap) which contains the pilot vent valve.

AIR BARREL

The cylindrical section of the air drive, between the two air caps, that guides the air piston and provides a surface for the piston seal.

AIR PISTON

The low pressure piston in the air drive that connects to the gas plunger/piston and provides the reciprocating (back and forth) motion needed for compressing gas to produce pressure and flow.

PILOT FILL VALVE

The normally closed pilot valve, located in the valve end cap that pressurizes the pilot chamber when actuated open by the air piston.

PILOT VENT VALVE

The normally closed pilot valve, located in the pilot vent end cap, that vents the pilot chamber when actuated open by the air piston.

AIR CYCLING VALVE

The valve assembly used to direct the flow of air alternately to one side of the air piston and then the other, to produce the reciprocating (back and forth) motion needed to make the booster function.

SLEEVE

The tubular portion of the cycling valve that contains the "porting" holes to direct the air to its proper destination, based on the position of the spool. This sleeve is sealed against "lands" in the valve end cap to partition the flow passages.

SPOOL

The moving portion of the air cycling valve that is controlled by the pilot valves pressurizing and venting the pilot chamber at one end of the spool. The "O" rings on the spool "partition" the flow to direct it to the proper passages in the sleeve to cycle the air piston.

FLOW TUBE

The flow tube routes the drive air from the valve end cap to the opposite end cap to provide pressure for the stroke towards the valve end cap. It also provides the path for venting the drive air from that side of the piston at the end of the stroke.

PILOT TUBE

The pilot tube connects the pilot chamber to the pilot vent end cap. When the air piston actuates the pilot vent valve open, it vents the pressure in the pilot chamber and shifts position of the cycling valve to reverse the direction of the air drive piston.

GAS SECTION

The section containing the gas barrel, plunger/piston, seal package and check valves. All parts of this section are exposed to the compressed gas. Therefore, all materials used must be compatible.

GAS BARREL/END CAP

The structural section of the booster. It contains the high pressure seal package and check valves.

PLUNGER/PISTON

The part, mechanically connected to the air piston that moves back and forth in the gas section of the booster to produce pressure and flow.

HIGH PRESSURE SEAL

The plunger, piston, or rod seal in the gas section that seals the pressure to contain the compressed gas. This seal may be a single part or a combination of parts, and is installed with bearings and backups as required to provide a "seal package" capable of resisting the pressure generated.

INLET CHECK VALVE

The check valve, located in the gas section that permits entrance of the gas on the "suction" stroke, and closes to trap gas in the gas section for the "boosting" stroke.

OUTLET CHECK VALVE

The check valve, located in the gas section, that permits gas to go into the downstream system during a "boosting" stroke and closes to prevent return of the gas during the "suction" stroke.

FLOW

The amount of gas forced into the downstream system. The amount is usually stated in "standard cubic feet per minute" (SCFM), or "liters per minute" (LITERS).

COMPRESSION RATIO

The "ACTUAL" compression ratio is the number obtained by dividing the area of the air barrel I.D. by the area of the gas barrel bore diameter.

To obtain the "NOMINAL" compression ratio, a friction multiplying factor is applied. For example, if the "actual" ratio is 33, then the "nominal" ratio is 30 (33 x .9 factor). This number is normally used to determine maximum attainable pressure.

STALL

When the booster has reached its "maximum pressure". The air drive force is equal to the pressure force in the gas section. Under this condition, there is no "unbalance" of forces left to drive the booster, and it stops cycling. This condition is referred to as "stall", and can be used as an automatic "safety" limiter by proper setting of air drive pressure.

SEPARATION

A vented, sealed section located between the air drive piston rod seal and the gas section rod seal to prevent direct leakage from the air drive into the gas section. All HASKEL boosters have separation.

SINGLE-ACTING BOOSTER

A booster that takes in gas on one stroke of the cycle and discharges it on the other stroke.

DOUBLE-ACTING BOOSTER

A booster designed to discharge gas on both strokes of the cycle. Depending on the check valve arrangement, the input (suction) of boosted gas can be on both strokes or only one.

TWO STAGE BOOSTER

A booster that has two pumping sections of different nominal ratios operating with a single air drive. These two sections are normally at opposite ends of the air drive. There is usually a "lower" ratio, high volume end for maximum displacement, and a "higher" ratio low volume end for generating final pressure.

SINGLE ENDED GAS BOOSTER

A booster which has the gas section only on one end of the air drive. It may be single acting (as in the "AG-15”) or double acting (as in the "AGD-4”).

DOUBLE ENDED BOOSTER

A booster having gas sections on both ends of the air drive. It may be "Single Stage" (as in the AGD-15) or "Two Stage" (as in the AGT-15/30).

UNSWEPT VOLUME

The minimum volume left in the gas section on completion of the compression stroke. This volume will normally be at system pressure when in operation. (The minimum volume is due to clearances, porting, and check valves.).

VOLUMETRIC EFFICIENCY

Gas is compressible. Because of the "unswept volume" in the gas section, it is impossible to "inhale" the actual displacement of the booster. This volume must expand enough to lower the pressure below supply pressure before new gas can enter the gas section. As the system (outlet) pressure increases, the "loss" of effective displacement per cycle increases, and the "volumetric efficiency" decreases. When the efficiency becomes "zero", the inlet/outlet pressure ratio has reached its maximum and it will not transfer gas even though it may still continue to cycle.

MAXIMUM COMPRESSION RATIO

Because of the "volumetric efficiency" effects due to the gas compressibility and the "unswept volume", maximum pressures attainable with gas boosters are not completely defined by the nominal booster ratio and the air drive pressure. The "Maximum Compression Ratio" is defined as the ratio at which the "volumetric Efficiency" becomes "zero".

INTERSTAGE STALL

Occurs only on "Two Stage" boosters when the "first stage" stalls because it cannot transfer its gas into the "second stage" without reaching stall pressure. Gas will increase in pressure in proportion to the amount it is compressed and if the supply pressure to the first stage is too high, the compression ratio between stages can result in an interstage pressure that exceeds the capability of the first stage. The booster will then stop cycling.

Interstage stall does not happen suddenly. When pressurizing a receiver from a gas supply, the booster will slow down as the system pressure approaches the stall pressure of the first stage. It will only stall when the system pressure exceeds that value, because the second stage is still able to discharge some gas into the system until stall pressure is reached.

MAXIMUM SUPPLY PRESSURE

Applicable only to "Two Stage" "Double Ended" gas boosters. The maximum supply pressure is the pressure which will result in "Interstage Stall" at the design operating conditions. For practical application, it is best not to exceed 75% of this pressure in actual service in order to maintain reasonable flow rates.