After the rocket engine has been fabricated, several check-out tests and flow calibrations should be made prior to testing with live propellants.
Connect the engine cooling jacket to a readily available source of pressurized water (such as lawn or house supply; pressure should be 50-100 psi with no flow). Attach a pressure gauge to the outlet port of the jacket and open the water valve, allowing water to fill the jacket. Observe the jacket and engine for leaks. There should be no leaks.
A similar pressure check should be performed on the fuel manifold of the injector. Since the injector face is not easily blanked off, perform this test by flowing water through the injector. Use a filter in the vater line to avoid plugging the small fuel injection holes. Use a pressure gauge attached to the water line as near to the injector fuel entry port as possible. There should be no leaks.
The water flow rate through the engine cooling jacket should be determined for various inlet pressures. Use a bathroom or other available scale to weigh, in a container, water flowing through the engine over a timed period. Water pressure can be measured either at the entrance or exit of the cooling jacket. Attach a flexible hose (garden variety will do) to the outlet of the cooling jacket and start water flowing through the jacket at the desired pressure. Once steady flow has been achieved quickly move the hose outlet into the catch container for a period of 30 seconds, then quickly remove the hose from the container. Use a stop or sweep second watch for the timing and be accurate! Obtain the net weight of collected water by subtracting from the weight of the filled container its empty weight. Divide the net weight by the time during which water was collected and the result will be water flow rate in lb/sec. This operation should be repeated several times at different pressures to obtain the flow characteristics of the coolant jacket. If insufficient water pressure is available to achieve the design water flow rate, check the size of tubing or hose used between the water source and the engine; it may be restricting the water flow rate. Check also the size of the flexible duct hose used. If these tests show that greater pressure is required to achieve the desired flow rate, a different source of cooling water may be required. Under extreme conditions, an air-presurized water tank or a motor-driven pump may be required. Another solution is to disassemble the engine and re-bore the outer shell to open up the water flow passage. Material should NOT be removed from the combustion chamber/nozzle.
Flow rate tests of the injector, using water, can be performed in a manner similar to the cooling system calibration, although their worth is questionable. The flow characteristics of water and the hydrocarbon fuels are different, so that a water calibration is not directly comparable to what will occur when fuel is used. However, the pressure drop required to flow a given quantity of water will provide some indication of how closely design objectives were achieved. This test should be conducted in the same manner as the cooling water calibration test except that the flow time should he long enough to accumulate at least ten pounds of water.
After the test stand and operator's area are completed and components installed, tests should the conducted to determine that no gas or liquid leaks will occur when actual propellants are used. Fill the tank with clean water. Cap off the fuel and oxygen lines where they would normally attach to the engine. Pressurize the system to 100 psi and check for leaks. A soap solution can be used to check around all fittings and seals. Soap bubbles indicate the presence of a gas leak. If no leaks are present, increase the pressure to 200 psi and repeat the detection procedure. Continue this procedure until the test stand operating pressure is reached and no leaks are present. Depressurize the system and refill the fuel tank with clean water. Attach the rocket engine to its test mount and connect all tubing. Pressurize the stand in the normal manner and practice the ignition and operating sequence using water as fuel (gaseous oxygen can safely he used in these tests, if desired). If no leaks develop, empty the fuel tank of water and dry by flushing with nitrogen gas for several seconds. The engine and test stand are now ready for their first hot firing.