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
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.
Valves
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.
Visor
The visor is a flat sunshade and is
usually movable. It is attached to the interior of the car at the top of
the windshield. Visors protect the eyes of the driver and passengers
from the sun's glare.
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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