Gas booster construction and function

Gas booster pumps are usually piston or plunger compressors.A single-acting, single-stage booster is the simplest configuration, consisting of a cylinder designed to withstand operating pressure and a piston driven back and forth within the cylinder.The cylinder head is equipped with supply and discharge ports to which supply and discharge hoses or pipes are connected,with a check valve on each port restricting flow in one direction from supply to discharge.When the supercharger is deactivated and the piston is stationary, gas will flow from the intake hose,through the intake valve and into the space between the cylinder head and the piston.If the pressure in the outlet hose is low,it will flow out and go wherever the outlet hose is connected.This flow will stop when the pressure equalizes, taking into account the valve opening pressure.Once the flow stops, the supercharger is activated,and as the piston recedes along the cylinder, the volume between the cylinder head and the piston crown increases, the pressure in the cylinder drops,and gas flows in from the intake port.During the return cycle, the piston moves towards the cylinder head, reducing the volume of the space and compressing the gas until the pressure is sufficient to overcome the pressure in the outlet line and the opening pressure of the outlet valve.At this point, gas will flow out of the cylinder through the outlet valve and port.There will always be some compressed gas left in the cylinder and head space at the top of the stroke.The gas in this "dead zone" expands on the next intake stroke, and only after it falls below supply pressure does more supply air flow into the cylinder.The ratio of the volume of the cylinder space to the dead space when the piston is fully wihdrawn is the "compression ratio" of the supercharger, also referred to herein as the "boost ratio".The efficiency of the supercharger is related to the compression ratio.When the air supply pressure ratio is lower than the boost ratio, the gas is delivered. When the intake pressure ratio increases, the delivery volume decreases..When there is no differential pressure, the delivery rate starts out very close to displacement and then decreases steadily until the pressure ratio reaches the maximum boost ratio when there is no effective delivery. 

Compression of a gas results in an increase in temperature.The heat is mainly removed by the compressed gas, but booster components are also heated by contact with the hot gas.Some boosters are cooled by water jackets or external fins to increase convective cooling of the surrounding air, but smaller models may not have special cooling facilities at all.A cooling unit would increase efficiency,but would be more expensive to manufacture.Boosters used with oxygen must be made of oxygen compatible materials and use oxygen compatible lubricants to avoid fire.

Configurations

• Single Stage,single Acting:There is a booster cylinder that pressurizes gas in one direction of piston movement and refills the cylinder on the return stroke.

• Single-stage double-acting:There are two pressurized cylinders,which work alternately,one pressurizes and the other inflates. Each cylinder is pressurized directly from the gas source, and the gas delivered by each cylinder is mixed at the outlet.The cylinders work in parallel and have the same bore diameter.

• Dual Stage,Double Acting:There are two cylinders, working alternately, one pressurizes the gas and the other supplements it, but the second stage has a smaller aperture,filled with the gas pressurized by the first stage, and carries the pressurized gas farther.The stages run in series and the gas passes through them in turn.

Power sources

Gas boosters can be driven by electric motors, hydraulics, low or high pressure air, or manually by a lever system.

Compressed air

Those powered by compressed air are usually linear drive systems in which a cylinder directly drives a compression piston, usually in a common housing separated by one or more seals.A high pressure pneumatic drive might use the same pressure as the output pressure to drive the piston, while a low pressure drive will use a larger diameter piston to increase the applied force.

Low pressure air

A common arrangement for low-pressure pneumatic boosters is that the booster piston is directly connected to the drive piston on the same centerline.The cross-sectional area of the low-pressure cylinder is much larger than that of the high-pressure cylinder, which is proportional to the pressure ratio between the driving gas and the pressurized gas.This type of single-acting supercharger has a booster cylinder at one end of the power cylinder, and double-acting superchargers have a booster cylinder at each end of the power cylinder,with a drive piston and a booster piston in the middle of the piston rod at each end.Oxygen boosters require some design features that may not be necessary in less reactive gas boosters. It is necessary to ensure that drive air (which may not be clean enough to come into safe contact with high pressure oxygen) does not leak through the seals into the pressurized cylinder,or that high pressure oxygen does not leak into the drive cylinder.This can be achieved by providing a space open to atmosphere between the low and high pressure cylinders, and the piston rod being sealed on each side it passes through the space. Any gas leaking from either cylinder through the rod seal escapes harmlessly into the surrounding air.A special case of a gas-powered supercharger is one in which the supercharger uses the same gas supply that powers the supercharger as the gas to be boosted.This arrangement wastes gas and is best used to provide a small amount of high pressure air when a large amount of low pressure air is already available.This system is sometimes called a "bootstrap" booster.