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Vacuum Hoses and Motors Vacuum lines are a series of hoses, or tubing, to the intake manifold. These hoses supply vacuum to various components of the engine, such as the emissions control system. Most air conditioning systems have vacuum motors to open and close the doors on the air conditioning ducts. A vacuum motor is just a small diaphragm with connecting rods to activate the valves of the system. They have the advantages of simplicity and quietness.

Vacuum Pump Most of the fuel pumps have a vacuum booster section that operates the windshield wipers at an almost constant speed. The fuel section then functions in the same way as ordinary fuel pumps. One difference is that the rotation of the camshaft eccentric in the vacuum pump also operates the vacuum booster section by actuating the pump arm, which pushes a link and the bellows diaphragm assembly upward, expelling air in the upper chamber through its exhaust valve out into the intake manifold. On the return stroke of the pump arm, the diaphragm spring moves the bellows diaphragm down, producing a suction in the vacuum chamber. The suction opens the intake valve of the vacuum section and draws air through the inlet pipe from the windshield wipers. When the wipers are not operating, the intake manifold suction (vacuum) holds the diaphragm up against the diaphragm spring pressure so that the diaphragm does not function with every stroke of the pump arm. When the vacuum is greater than the suction produced by the pump, the airflows from the windshield wiper through the inlet valve and vacuum chamber of the pump and out the exhaust valve outlet to the manifold, leaving the vacuum section inoperative. With high suction in the intake manifold, the operation of the wiper will be the same as if the pump were not installed. When the suction is low, as when the engine is accelerated or operating at high speed, the suction of the pump is greater than that in the manifold and the vacuum section operates the wipers at a constant speed.

Valve  A device through which the flow of liquid, gas, vacuum, or loose material in bulk may be started, stopped, or regulated by a movable part that opens, shuts, or partially obstructs one or more ports or passageways. A valve is also the movable part of such a device.

The valve opens and close the valve ports. If the ports were always open, the fuel exploded in the combustion chamber would leave through the ports. The explosion has to be kept in the combustion chamber to push the piston down. The valves are set up to open and close at exactly the right moment. One lets the fuel mixture in and closes. After the fuel explodes and pushes the piston down, the other valve lets the exhaust out.

Valve Body  Part of the valve assembly containing plungers, pistons, springs, etc.

Valve Clearance  The clearance between the valve tip (the end of the valve stem) and the rocker arm or tappet. The valve clearance is measured when the valve is closed.

Valve Cover The valve cover covers the valve train. The valve train consists of rocker arms, valve springs, push rods, lifters and cam (in an overhead cam engine). The valve cover can be removed to adjust the valves. Oil is pumped up through the pushrods and dispersed underneath the valve cover, which keeps the rocker arms lubricated. Holes are located in various places in the engine head so that the oil recirculates back down to the oil pan. For this reason, the valve cover must be oil-tight; it is often the source of oil leaks. One way to determine if your valve cover is bent is to remove the gasket and put the valve cover back on to the cylinder head. When the valve cover and cylinder head come into contact, the cover should sit flat. If it rocks, it is bent. A symptom of a bent or leaking valve cover is a pinching of the valve cover gasket. This means that the gasket is sealing one area and not sealing another area. This condition produces a leak; oil could be leaking down the side of the engine. Some valve covers are hard to access, because they are covered with other engine parts. Chronic valve cover leakage can sometimes be fixed by using two gaskets glued together instead of using just one.

Valve Lifter The valve lifter is the unit that makes contact with the valve stem and the camshaft and rides on the camshaft. It opens the valve when the cam lobes push it upwards. The engine oil comes into the lifter body under pressure. It passes through a little opening at the bottom of an inner piston to a cavity underneath the piston. The oil forces the piston upward until it contacts the push rod. When the cam raises the valve lifter, the pressure is placed on the inner piston, which tries to push the oil back through the little opening. It can't do this, because a small check valve seals the opening. When the cam goes upward, the lifter solidifies and lifts the valve. Then, when the cam goes down, the lifter is pushed down by the push rod. It adjusts automatically to remove clearances.

Valve Ports Valve ports are openings in the cylinder head. Intake ports let the fuel mixture into the cylinder head, and exhaust ports let the exhaust out.

Valve Seals The valve seal is a unit that goes over the end of the valve stem. It keeps excess oil from getting between the valve guide and the valve stem.

Valve Springs The valve springs keep the valves closed tightly against their seats until the cam opens the valve. After the cam turns (releasing pressure), the valve springs close the valves.

Valve Train The collection of parts that make the valves operate, allowing fuel intake, compression and exhaust. Includes the camshaft(s) and all related drive components, and the various parts that convert the camshaft's rotary motion into reciprocating motion at the valves.

See The Internal Combustion Engine

Vane A thin plate that is affixed to a rotatable unit to either throw off air or liquid, or to receive the thrust imparted by moving air or liquid striking the vane. In the first case it would be acting as a pump and in the second case as a turbine.

Vernier Caliper  A precision measuring instrument that measures inside and outside dimensions. Not quite as accurate as a micrometer, but more convenient.

Viscosity  The thickness of a liquid or its resistance to flow.

Volt  A unit for expressing electrical "pressure" in a circuit. One volt that will produce a current of one ampere through a resistance of one ohm.

Voltage Regulator  The voltage regulator controls voltage and current output of the alternator by automatically cutting resistance in or out of the field circuit to keep it in a safe value. Varying the resistance alters the amount of current passing through the field. When the battery becomes fully charged, the resistance is cut into the field circuit and the charging rate is decreased. In electromagnetic regulators, the voltage regulator unit limits voltage output by controlling the amount of current applied to the rotating field. The field relay on these regulators connects the alternator field windings and voltage regulator windings directly to the battery. The conventional cutout relay unit has been eliminated by the diodes in the alternator. The current regulator has also been eliminated by the current-limiting characteristic of the alternator design. Basically, in a transistorized or an electronic regulator, the transistor is switched on and off to control the alternator field current. The frequency of switching depends on the alternator speed and accessory load, with the possibility that the on-off cycle may be repeated as often as 7000 times per second. The transistorized units have a voltage limiter adjustment. The electronic units are factory calibrated and sealed. They are also nonadjustable.


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The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

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