In this section we shall discuss the auxilliary equipment
needed to operate the rocket engine, the installation of this
equipment, and its safe use in engine operation.
Feed System
The feed system for amateur rocket engine testing consists of
a tank to store the liquid fuel, a regulated supply of high pressure
nitrogen gas to force the fuel from the tank into the engine, a
regulated supply of high pressure gaseous oxygen, and a control device
for regulating the propellant flow rates. A typical pressurizing feed
system is shown schematically in Figure 10.
Feed System Components
The components of a rocket engine feed system are precision instruments designed to handle gas and/or liquids at high pressure. While many of the components suitable for use in amateur rocket feed systems are readily available from welding or automohile parts suppliers, they are usually relatively expensive. The amateur builder should expect the assembly of the feed system to be an expensive project which, however, need be done only once. The use of quality products, made to do the job or very carefully modified and pre-tested, is mandatory for safe operation of amateur rocket engines.
Gases stored in cylinders at high pressure (usually about 1800 psi) are readily obtained from any bottled gas supplier or from many welding suppliers. Special fittings with nonstandard threads are used to prevent use of incorrect equipment with the cylinders. Although cylinders can be purchased, they are usually rented and then returned to the supplier for recharge at a nominal fee. High pressure gas cylinders should never he dropped or mishandled. Cylinders should be stored so they cannot fall over or inadvertently roll; the best way of securing is to chain or strap the cylinders to an appropriate stand or worktable. When cylinders are not in use the cap should be kept on to protect the cylinder valve. Several suppliers of high pressure gases publish instruction books on the care and use of high pressure cylinders (see Bibliography); the amateur is encouraged to read and follow these professional instructions.
Nitrogen is an inert gas compatible with all normally available materials. The amateur builder will have little dificulty with materials of construction for nitrogen but must be careful that all components are suitable for high pressure service. Cleanliness of components is important for proper and reliable operation,
Oxygen will not itself burn but does vigorously support the rapid combustion of almost all other materials. The amateur must be concerned not only with suitablility of components for high pressure service but also must use only components that are made from oxygen compatible materials and that are cleaned for oxygen service. All items, including lines, fittings, valves, regulators, etc., MUST be absolutely free from oil, grease, and similar contaminants. Thorough cleaning of all items in solvent, followed by a complete rinse in acetone, is an absolute must. Orders for commercial items should he marked to indicate their intended use with high pressure gaseous oxygen. Many commercial suppliers of valves and regulators offer a special service for cleaning their products for oxygen service. The amateur should avail himself of these services whenever possible, even though they will add slightly to the initial cost of the component.
When cleaning components with solvent or acetone, the amateur builder should observe all rules of safety applying to these chemicals. They are toxic and easily ignited. Cleaning should be done outside and away from huildings, fires, or other possible ignition sources. These fluids should not be stored indoors but in vented lockers away from main buildings.
The fuel tank is a closed vessel which contains the liquid fuel at moderate pressure (300-500 psi). Tanks of various sizes and shapes, made from carbon- or stainless steel, are offered to the public from war surplus outlets. The amateur builder should be very careful if he decides to use such a tank. They should not be modified since in nearly all cases they are thin wall pressure vessels made for aircraft service, and additional outlets or welding to the tank wall could seriously weaken the tank. In all cases the tank should be hydrostatically tested to at least 1 1/2 times desired operating presure before use in the rocket engine feed system.
The amateur may build (or have built) a tank especially for his requirements. Seamless tubing or pipe (mild steel or stainless steel) with welded flat end plates makes an excellent tank. Outlet ports are easily tapped in the flat end plates, The tank wall thickness is given by Equation (22)
The fuel tank should contain enough ports, or the tank plumbing should be so arranged, that a safety relief valve (either spring loaded or a burst disc), gas inlet port, load and vent port, and fuel outlet and drain are available. Many of these functions can be incorporated as part of the gas inlet and fuel outlet plumbing so that only two ports, one on each end of the tank are required.
| Fabrication | Index | Test Stand |
