Note: Descriptions are shown in the official language in which they were submitted.
11)36444
This invention relates to an improvement in
a Carburetor Inlet Valve Seat and more paxticularly
to the material and design of a valve seat which co-
operates with an inlet valve to control the amount of
fuel which can reach a control chamber in a carburetor
from the ~uel source.
It will be appreciated that all carburetors
must receive a supply of fuel from a fuel tank. Some-
times this fuel is ~urnished to the carburetor by a
gravity feed from a tank. In other instances, it is
furnished by a pump which moves the fuel from a tank
to the carburetor. In either case there is generally
a fuel head at the carburetor which is controlled in
its flow to the interior of the carburetor by an inlet
valve.
It has been desirable in valves of this kind
to avoid a metal-to-metal contact. In a larger fl~at
carburetor illustrated in a U. S. patent to Tuckey
3,265,050 (Aug. 9, 1966), there is shown a resilient
tip on the inlet valve which cooperates with a valve
seat in a threaded insert. In other disclosure3 as
illustrated in the U. S. patents to Schneider 3,361,120
(Jan. 2, 1968) and 3,690,304 (Sept. 12, 1972), there is
shown a metal valve seat insert carrying a plastic valve
seat which c~operates with a metal inlet valve.
10;~6~44
Recent dsvelopments in the past few years
relative to smaller engines and more limited space
resulting particularly from chain saw design, the
space available for the inlet valve has been greatly
reduced. It has been necessary) therefore, to drill
the valve seat directly into the carburetor body as
illustrated, for example, in a U. S. patent to Tuckey
3,758,084 (Sept. 11, 1973). The valve seat has thus
been a metallic valve seat formed by a portion of the
carburetor housing; and even when a resilient tip on the
valve was utilized to prevent wear, there were prob-
lems with the design due in part to the inadvertent
porosity of the castings which would cause leaks. The
machining of the seat in the casting very often involved
three separate operations to get a proper finish and,
yet, in instances where porosity was revealed by these
machining operations, the casting would have to be com-
pletely rejected. One attempt to solve this problem is
illustrated in a U. S. patent to Donovan 3,791,632
(Feb. 12, 1974).
The present invention is intended to be an
improvement on the previous inlet valve designs which
solves the problems of the casting porosity, and it
~0364~L
eliminates the expensive machining as well as reduces
the cost of the entire assembly. In addition, the
present system eliminates the need for a plastic tip
on the inlet valve. Thus, the present invention eli-
minates machining, reduces the cost of the inlet valve,and solves the problem of the sealing of the car~uretor
housing in case of unwanted porosity.
Other objects and features of the invention
relating to details of construction and operation will
be apparent in the following description and claims in
which the principles of operation are set forth to-
gether with the best mode presently contemplated for
the practice of the invention.
DRAWI~GS accompany the disclosure and the
various views thereof may be briefly described as:
FIGURE l, a sectional view of a carburetor
in which the invention may be used.
EIGURE 2, an enlarged view of the valve seat
insert prior to assembly.
1~6~4
With reference to the drawings, in FIGURE 1,
a sectional view of a carburetor is shown. This car-
buretor is described in detail in U. S. Patsnt No.
3,758,084, above referenced. It consists basically
of a carburetor body 20 having a top plate 2~ which
formsO in connection with the body, a pumping chamber
24 which furnishes fuel under pressure to a fuel inlet
chamber or port 26. A venturi or mixing chamber 28
i8 provided in the usual mannex and at the bottom of
the carburetor housing is a flexible diaphragm 30
which contaols a spring-backed lever 32 which acts
upon an inlet valve 40 which moves axially in a
drilled bore 42 in the body. The valve 40 is fluted
to allow the passage of fuel around it and it has a
tipped portion 44 which cooperates with the valve
seat to be described.
The valve seat 50 is shown in an enlarged
view ~FIGURE 2) in unassembled condition, and it is
shown assembled in FIGURE 1 in the drilled bore 42.
This valve seat is preferably formed of fuel resistant
synthetic rubber material or its equivalent. The
insert i~ a cylindrical element which has a stepped
-4-
~ 3~4~9~
outer diameter, the smaller diamet r 52 being at the
bottom of the unit and the larger diameter 54 being
at the top, ~here being tapered portions 56 and 58
at each end of the enlarged portion. The insert
has a central passage 60 extending from end to end
and directly adjacent the upper periphery of the
passage 60 is an annular rim 62.
When the insert 50 is installed in the
drilled bore 42, it i5 forced upwar~ly into the bore
which has a diameter substantially equal to the small-
er diameter portion 52. This cause~ a compression
displacement Qf the larger portion 54 so that it
seals against the walls of the drilled bore 42 and
also has a snug fit in relation thereto. Also during
the assembly the annular portion 62 is forced up
against an end wall 64 of the drilled bore 42 where
it surrounds a short inlet passage 66 leading from
the inlet port 26 to the drilled bore 42. Thus,
there will be a pressure seal directly around the
bottom of the short passage 66 which will prevent
fuel from bleeding and exerting a dislodging pressure
over the entire top surface of the insert 50. In the
444
operation, of course, the inlet valve 40 will be
regulated in its position by the control diaphragm
30 in the usual way and the tapered point of the
valve will cooperate with the lower end of the
center pas~age 60 which serves as a valve seat 70.
Thus, it will be seen that the molded in-
sert 60 can be produced very inexpensively in large
quantities and easily installed in the top of the
drilled bore 42 against the end wall 64. This avoids
expensive machining and will seal porosity that might
exist which would allow fuel to pass from the port 26
to the drilled passage 42 below the insert. It also
seals agai~st the end wall to prevent pressure dislodge-
ment and it inherently provides the necessary slightly
resilient valve seat which cooperates with the valve
tip 44.
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