Kohler l654 Service-Handbuch - Seite 14

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GAS SYSTEMS

Natural

gas supplied

from

main transmission

line is normally

received

at pressures

not greater

than 51) pounds

per

square

inch (psi)

while with LPG,

which

is Butane or Propane

or usually

a mixture

of the two gases,

the pressure

may go as high

as 180-200

psi depending

on the mix ratio and

tempera-

ture.

To be used by the engine

the pressure

must be reduced

to.ounce

values.

The reduction

is nor-

mally

accomplished

in two stages

by a primary

regulator

which

reduc

line pressures

to about 6 ounces

per square

inch and a secondary

low pressure

regulator

which further

reduces

the pressure

in accord-

ance with engine demand.

The primary

regulator

is often furnished

by the fuel supplier.

The fuel

supplier

should also insure

that gas pressure

is sufficient

to operate

the primary

regulator.

If pressure

drops

too low,

the regulator

may not function

at all.

While propane,

for example,

tends to maintain

some vaporizing

pressure

even at temperatures

down

to -20'

butane returns

to liquid

state and

offers

little

or no vapor pressure

when the temperature

drops

to freezing

or 32O F.

For this 'reason,

fuel suppliers

usually

supply LPG

of higher

butane content

in hot weather

but will alter

this to a higher

percentage

of propane

during cold weather.

If this ratio

is not changed,

starting

and operating

difficul-

ties may be encountered

in cold weather.

Straight

gas and combination

gas/gasoline

systems

are used.

The combination

system

uses a gas

mixer

or adapter

attached

to a standard

gasoline

carburetor.

and regulators

are discussed

in the following.

Some common

carburetors,

adapters,

GAS CARBURETORS

- ADAPTERS

In a venturi

type carburetor,

the gas nozzle

is located

at the point of greatest

pressure

drop inside

the venturi.

This creates

a suction within that nozzle

that varies

with changing

rate of air flow and

causes

a greater

volume

of gas to be metered

at heavier

loads and a lower

volume

at lighter

engine load.

The throttle

valve

regulates

the rate of air flow through the carburetor.

this valve

is wide open and offers 'little

restriction

to air flow.

When an engine is at top speed,

Closing

the throttle

causes

a decrease

in air flow and lowers

engine

speed and power.

As the valve

closes,

it reduces

pressure

through the

venturi

and past the fuel nozzle.

On engines

with the gasoline

carburetor,

an adapter

with venturi

is installed

between

the carbure-

tor and air cleaner.

The adapter

consists

of a gas jet and venturi.

Accurdte

metering

of the gas is

accomplished

by load and starting

or idle adjustment

screws

in the body of the adapter.

Most gas carburetors

are simple

devices

having only one moving

part--the

throttle

shaft and

plate (or butterfly

valve

as it is sometimes

called).

Because

of this,

they should require

very little

attention

and readjustment

should seldom

be needed.

If needles wear out or venturi is damaged,

these

IDLE FUEL

BREATHER.

TUBE TO

VALVE COVER

IDLE

SPEED

ADJUSTMENT

JdAIN FUEL

SECONDARY

GAS

REGULATOR

(MODEL UN)

-=--ii&

OIL BATH

TYPE AIR

CLEANER

(3/4"

NPT

FROM PRIMARY REGULATOR)

FIGURE 4-8 -- TYPICAL STRAIGHT GAS FUEL SYSTEM