TROUBLES OF MOTOR-CAR FUEL FEED

Wanganui Chronicle, Volume LXXXII, Issue 19443, 31 October 1925, Page 18 (Supplement)

TROUBLES OF MOTOR-CAR FUEL FEED

DIFFERENT SYSTEMS DESCRIBED. WHAT EVERY OWNER OUGHT TO KNOW. We can compare the fuel feed system of a motor with the water system of a large city. The water is held in a reservoir some distance away, and is pumped' through large mains to the city, where it is distributed to individual stations. Before the water loaves the reservoir it is strained or cleaned in some manner, so that dirt in large quantities will not be forced along with it. Auxiliary strainers or cleaners are used at the pumping stations and elsewhere. It is obvious that a large amount of dirt and sediment collecting in a small pipe will clog it. Tn the fuel feed system of a motor there is a main tank, usually at the rear of the car, corresponding to the reservoir, a pipe leading from this tank to the carburettor or to a smaller tank, called a vacuum tank, and from the latter another pipe to the carburettor. In the main tank, vacuum tank, and carburettor there are traps and strainers to catch dirt and water, as both of these must be periodically removed from the system so that large quantities never will be present. If the owner is not familiar with the location of sediment traps and strainers, he should ask the service manager to point them out, for it is a matter of minutes removing and replacing tho parts. The operation of the ' ear with any degree of smoothness I depends in a large measure upon the ' free flow of fuel from the main tank, ; through the piping into and out of the : vacuum tank, and into and out of the ! carburettor. Unless the fuel feed sysi tern is working properly the engine may misfire, lack power, refuse to pull up a grade, or even refuse to pull at all. The Gravity Feed. System. The gravity fuel system uses a main tank, which is sometimes under the seat of the car. and sometimes between the dash and the bonnet, and a pipe from this tank to the carburettor. That is all there is to the whole system. The fuel flows by gravity into the carburettor. A small hole in the cap of the main tank permits air to enter, and it is this 14-odd pounds atmospheric pressure that causes tho fuel to be forced out of the tank. The reason the tank is placed under tho seat or below the dash is to provide sufficient “head,” so that the fuel will flow downward into the carburettor. If the tank were below tho carburettor, no fuel would flow at all, because without added pressure fuel will not flow of itself in an upward direction. In a badly-designed gravity system, if the car is going up a steep grade and there is too little fuel in the tank, feeding

may stop and the car will be stalled. Also, if there is not enough benzine in the main tank and the car tilts to one side, as on a heavily-crowned road, the fuel may not feed because the feed pipe will be uncovered. At the bottom of the main tank there is a sediment trap flitted, with a drain cock. The Vacuum Tank System. In order to locate the main petrol tank at the rear and under the level of the carburettor, it is necessary to use some means of forcing the fuel out of tho tank. This can be done by added pressure in the main tank or by means of a vacuum tank. This tank is mounted generally on the engine side, of the dash, and has three pipes attached to it—one to the intake mani-fold,-one to the carburettor, and one to the main fuel tank. The vacuum in the intake is transferred to the tank, and with atmospheric pressure existing in the main tank, and practically none in the vacuum tank, the fuel flows into the latter tank. Tho carburettor is .fed by gravity from the vacuum tank. The vacuum tank has two chambers; the upper chamber is the filling chamber, and the lower the emptying one. Between the two chambers is a partition containing a flapper valve on the lower side. The suction of the piston on the intake stroke creates a vacuum in the upper chamber. This closes the flapper valve between the two chambers, and in turn draws petrol from the main supply tank. The sucking of petrol into this upper chamber operates the float valve. When this float has risen to a certain point it automatically cuts off the suction valve, and opens the air valve. This open-air or atmospheric valve creates an atmospheric condition in the upper chamber

which permits the flapper valve to open and the fuel to flow into the lower chamber.

Tho lower chamber is always open to atmospheric conditions, so that the filling of the upper chamber in no way interferes with an uninterrupted flow of petrol from tho lower chamber to tho carburetter. The suction valve opens and closes the connection to the intake manifold. Through this action, a vacuum is extended to the vacuum tank. The air valve prevents an atmospheric condition in the upper chamber. When the suction valve is open, the suction is drawing benzine from the main reservoir, the air valve being closed. When the suction valve is closed, then the air valve must be open, permitting the atmospheric condition which is necessary in the upper tank, in order to allow the fuel to flow through the flapper valve into tho lower chamber.

In the small tank there is a lever at the top, which is controlled by the float valve, and a short lever slipporting the valves, which is actuated by the longer lover through a spring connecting their free ends. The two levers are pivoted on the same fulcrum in such a way that tho spring is above the fulcrum when the float is high, and below it when the float is low. The angularity of tho spring in either position insures a positive closing of one of tho two valves. Pressure Feed System.

In the gravity and vacuum feeds, the petrol in tho main tank is forced out by atmospheric pressure, while in the so-called pressure feed tho main tank is completely healed, and air pressure is tused to push tho petrol to tho carburettor. In the pressure system, the main tank may be placed at tho rear at a point above or below the carburetter —generally much lower. There are two pipes Tuning to the main tank, one feeding fuel and tho other permitting air to bo forced into the tank. A hand pump on tho dash is used to provide initial pressure, as when the ear has been standing for some time, and the pressure in the tank has been lost. After the engine starts, a pump, driven by the engine, supplies the air pressure, and when tha’. pressure has reached a predetermined point, ’ generally two pounds, a valve automatically releases additional air, thus maintaining constant pressure. A pressure gauge on the dash indicates the pressure on the fuel in the main tank. Importance of Cleanliness. In all systems described, cleanliness is essential. The strainers or traps must be emptied and cleaned at least once a month during cold weather, and once every two weeks during warm weather. No matter how careful you may be in buying clean benzine, sediment is bound to collect in the fuel systems. Eventually it gets into the float bowl of the carburetter, where it interferes with the correct metering of fuel, and you get spitting, stalling, and other troubles. The gravity system is the simplest to care for, as there are no moving parts outside of the carburetter. The fuel pipe leading to the carburetter must have “easy” bends, for if there is a sharp one, a kink, it offers a lodging place for dirt. The kink itsUf is enough to restrict fuel flow, and the collection of sediment adds to this trouble. In a gravity system the carburettor should bo cleaned occasionally, a trap or plug generally being provided at the bottom of the tank or elsewhere is bound to start trouble. Naturally the fuel bill goes up, but what is more, if the leak is bad enough fuel flow is not correct. In the pressure feed system there may be two kinds cf leaks—air and petrol. If there is an air leak that the pump cannot compensate for tho carburettor will not be filled fast enough to supply the engine. It might run at slow speeds, but it will not accelerate well, nor will it climb grades. In the vacuum system, in addition to observing cleanliness and the other matters previously mentioned, the tank itself may need attention. Though rare, it sometimes happens that tho tank does not function correctly. It is possible to test tho tank by opening tho pet cock at teh bottom, and if more than half a pint of petrol flows out the system is performing properly.

Running the engine at slow speeds with an open throttle for a long time, such as in ascending a long, gradual hill, may reduce the vacuum to a sufficient extent that the tank will not fill, or this condition might result from dirt or foreign matter getting in and clogging the feed line to the tank. If it is a case of insufficient suction, duo to a leak in the suction line, this can always be overcome by letting the engine run with throttle closed for a few moments, after which sufficient sue-

tion will be created to fill the tank. In case the float valve leaks for any reason, which would cause an overflow of benzine from the tank, either through the vent pipe or some other portion, the inner shell can be taken out by removing eight screws at the top of the tank. The tank may then be filled with petrol, and will act as an ordinary gravity system, enabling the owner to drive to the nearest garage where the float may be repaired. Should the tank ever become empty, it may be filled by closing the throttle and cranking the engine. This will create a sufficient vacuum in the tank to fill it. If the tank has been allowed to stand empty for a considerable time, and does not readily fill when the engine is turned over, either sediment or dirt has accumulated under the flapper valve, or the valves are dry. To overcome this difficulty remove the plug at the top and squirt a little fuel into the tank. This will wash the dirt from the valve, and also wet the valves and cause tho tank to work immediately.

The market now offers various types of fuel cleaners or strainers, some employing chamois and some large wire screens. In the designs employing chamois, one must be sure that the area is sufficient so that it will permit the proper amount of fuel to filter through. Unless this is so one will get the equivalent of a partially-obstructed line. And in both types it is desirable that the fuel bo filtered in an upward direction. This assists in filtration, for it is natural for the particles of dirt to settle instead of flow upward. Whatever tho type selected, the installation of some straining device in the line is a step toward smooth operation and freedom from trouble.

TAKE CARE OF YOUR CAR ABUSE DOES NOT PAY. When a man invests sometimes as much as half a year’s salary in a motor car, he should have reason to expect good returns on his investment. But, the best car built is not intended to be misused, although it may stand an awful lot of it. Many owners misuse a car through ignorance of what is good for it, and what is bad for it, and misuse, therefore, is not always intentional. The modern car has been so simplified that there »is hardly any reason to plead ignorance in the proper care of it. The principal abuse arises in handling the car, for many will drive along for miles with several cylinders missing, disregarding entirely the stress which this places on the working parts of the engine. Others will disengage the clutch at the top of a hill as th y start the descent, putting the weight of the car, its momentum, and the increase in speed on the brakes when stopping suddenly at the bottom of the hill. Is it any wonder that brakes become defective and fail when most needed" Brakes are intended to retard the momentum of the ear, and gradually bring it to a stop, but they cannot be expected to function indefinitely without attention.

PETROL VAPOUR It is seldom realised that the vapour produced by petrol can flow for considerable distances. It is of a heavy nature, and it is, consequently, usually found close to the ground, and it is quite possible for a flame to flow back several yards to the source from, which the vapour is being emitted. In a recent case the driver of a dualpurpose vehicle was tilling the tank under the driver’s seat with petrol while an assistant was fitting steps at the back of the body, for the convenience of pasengers, by the light from a candle. It appears that the exhaust pipe was warm, and some of the petrol, spilling on to this, was rapidly turned into vapour, which flowed to the back of the vehicle, and was there ignited by the candle, with fatal results to the driver.