What To Do When The Vaccum Tank Fails

Poverty Bay Herald, Volume LXII, Issue 18817, 21 September 1935, Page 9

What To Do When The Vaccum Tank Fails

WHILE not quite us simple as gravity v* feed, or as relittblo as modern fuel-pump systems, the Vacuum tank is generally a very satisfactory method of supplying fuel t.O the engine, allowing the main tank to be placed at a low level at the rear of the chassis, where it is both safe and convenient for filling.. One advantage which it 'has over many fuel pumps is simplicity,. repair usually being a comparatively simple matter. Titers is oho inherent fault in vacuum tanks —they will not function satisfactorily if the engine is driven at full throttle continuously for some time. This is due to the low induction vacuum existing in such conditions, and the effect is most noticeable when hill climbing. Should failure occur at such, a time there is nothing to be done except to refill the, vacuum tank, and this can most easily lie done by allowing the engine to idle for a few minutes. Faults Which Can Be Remedied. Faults which can be remedied include petrol blockage, air leakage and mechanical defects occurring in. the valves or float, the latter causing either petrol starvation or flooding. If under normal driving conditions petrol fails to reach the tank, first disconnect the main fuel line, and see whether it is possible to suck petrol , tip freely from the main tank. Then ry unserew the petrol inlet elbow at the top of the vacuum tank, revealing a wire-gauze thimble. This thimble, ,which, is of coarse mesh, is intended only to stop large particles, and seldom gets completely choked. When it has been ascertained that there is no obstruction it becomes obvious that the necessary vacuum is not being formed inside the upper section of the vacuum tank to raise the fuel. First examine all joints and pipes. Any air leakage in either the vacuum pipe from the induction manifold, or the fuel pipe leading to the main tank, will cause trouble. The Best Test. Probably the best test is to pour some petrol into cither the carburettor or vacuum tank and start, the engine. Have the main fuel pipe disconnected where it enters tho main tank, and hold the finger over it. A distinct suction should be felt. In making this test pour hot more than about a cupful of fuel into the vacuum tank in order to start the engine. Alternatively the end of the main pipe may be dipped into a vessel filled with fuel, which will be sucked up rapidly if all is in order. To test whether failure* is due to an air leakage in the main, pipe repeat the test, working with the main pipe disconnected at the tank inlet elbow. For correct functioning not only must the elbows be firmly screwed into tho tank top, but the holding-down screws must be tight, the cork gasket in good condition and the suction pipe clear. If there is no air leakage some derangement of the interior mechanism is probable. If it is meroly stuck, as sometimes happens if tho tank has been empty for some time, a thump with tho hand may free it. Inside the tank there are two sets of valves, controlled, by a float, and also a flap valve, which allows the upper chamber to empty itself into tho lower, but prevents suction operating on the lower tank, which feeds to the carburettor, and is open to the air. These valves should snap promptly open and shut as the float is operated. One controls the suction line, closing as the float rises; while the other, which then opens, communicates with an air vent. ■Bucking at these two: points will determine whether the valves are seating properly. Flooding of the Tank Flooding of. the lank, which “drowns” the engine with fuel drawn down the suetion line, is due usually to a punctured float. It is an easy matter to replace the old float, but if a new one is not obtainable the old one can be repaired. Immerse the old float in boiling water and observe where the bubbles escape from the petrol inside it. Drive out the petrol by immersion in hot

water, making another small hole if necessary to speed up the process, and then repair the leaks by soldering them up. Be careful to use the least possible' quantity of soldier necessary for. a sound job. There are numerous designs of tanks, but all work on the same principle.