Bypass valve and visual indicator for a fuel system

A bypass valve 30 for a fuel supply system 10 of an aircraft. The bypass valve 30 has a housing 32 with a chamber 38 having an entrance port 34 connected to a pump 16 and an exit port 36 connected to a regulator 14. An end cap 44 which is screwed into the housing 32 to seal the chamber 38. A sleeve 46 which extends from the end cap 44 into chamber 38 has a series of radial openings 48 and 50 to communicate the exit port with the interior of the sleeve 46. A piston 58 is retained in the sleeve 46 by a retainer stop 68. A spring 64 acts on the piston 58 to move a face 66 against retainer stop 68 to separate the entrance port 34 from the exit port 36. When a predetermined pressure drop occurs across a filter 26, piston 58 moves and allows fuel to directly flow to regulator 14 without passing through filter 26. At the same time, the fluid pressure acts on the cylindrical body 76 of indicator 74 to move face 75 away from housing 32 and provide a visual indication that unfiltered fuel has entered the fuel system.

This invention relates to a bypass valve and visual indicator for an 
aircraft fuel supply system having a pressure differential responsive 
piston that moves to allow fuel from a source be directly supplied to a 
regulator without passing through a filter. Once the piston moves to allow 
fuel to directly flow to the regulator, an indicator moves to provide a 
visual indication of such movement and a corresponding need to evaluate 
the operation of the fuel system. 
U.S. Pat. No. 4,245,462 discloses a fuel system wherein fuel from a source 
or reservoir is supplied to a regulator by a pump. As shown in this 
typical system, fuel passes through a filter prior to being supplied to 
the regulator for distribution to the combustion chamber in the turbine. 
The need for clean operational fluid should be evident since dirty or 
contaminated fuel could cause valves to stick and as a result the 
regulator would malfunction. It is common for a regulator to have an 
electronic sensor which supplies a CPU and an indicator in the instrument 
panel of an aircraft with a readout of the quantity of fuel being supplied 
to the turbine. If the flow of fuel through the filter is reduced, the 
fluid pressure of the fuel supplied to both the regulator for distribution 
to the combustion chamber and as the operational fluid for operating the 
various components is reduced. As a result, such a reduction in pressure 
may have an adverse effect on the operation of the turbine. The electronic 
sensor is designed to provide the operator with a warning when the 
pressure of the fuel is reduced to a preselected level. Unfortunately, if 
this level is reduced while the aircraft is in flight, the power generated 
by the turbine could be reduced to a point where the operation of the 
aircraft is in peril. 
It is an accepted principle that it would be better to allow unfiltered 
fuel be supplied to the turbine than require the turbine to operate with a 
fuel whose pressure has been reduced to a level which may adversely effect 
the operation of an aircraft. 
The present invention relates to a bypass valve having a visual indicator 
in the fuel system for an aircraft which allows the output of a pump to be 
directly connected to a regulator if flow through a filter is restricted. 
The bypass valve has a housing with a piston located in a chamber for 
separating an entrance port from an exit port. A spring acts on and moves 
the piston against a retainer stop where the body of the piston overlaps 
the exit port to prevent fuel communicated from the pump into the chamber 
through the entrance port. The exit port is in communication with the 
conduit through which filtered fuel is supplied to the regulator. A 
projection that extends from the face on the piston is located in a groove 
of a cylindrical body of an indicator that is retained in the housing. The 
unfiltered fuel from the pump and the filtered fuel develop a pressure 
differential across the piston. As long as the force developed by the 
pressure differential is less than the force of the spring, the piston 
remains on the seated on the retainer stop and all fuel from the pump is 
supplied to the regulator through the filter. When the developed pressure 
differential force across the piston exceeds the spring force, the piston 
moves and fuel from the pump flows through the chamber from the entrance 
port to the exit port for distribution to the regulator without going 
through the filter. On the initial movement of the piston, a projection on 
the piston moves out of a retaining groove in the cylindrical body of the 
indicator. Thereafter, the fluid pressure of the fuel from the pump acts 
on the cylindrical body and moves a first end with respect to the housing 
to provide a visual indication of bypassed fuel. Contours on the 
projection of the piston insure entrapment of the retainer stop as fuel 
flows through the chamber in addition to directing the flow of fuel 
through the chamber such that cavitation and other flow created turbulence 
is either eliminated or substantially reduced to a point where it is not a 
factor. Later, when the aircraft has landed and the turbine shut down, the 
spring moves the piston against the retainer stop to again interrupt fluid 
communication between the entrance port and exit port. However, the 
projection that extends from the piston prevents the cylindrical body from 
re-entering the chamber and provide a continued indication that unfiltered 
fuel was supplied to operate the turbine. The cylindrical body can only be 
reset by a positive manual action of an operator. 
It is an object of this invention to provide a fuel system for an aircraft 
with a bypass valve having a visual indicator which would allow unfilter 
fuel to be supplied to operate an engine in an emergency condition. 
The inclusion of this bypass valve in a fuel system for an aircraft 
provides an assurance that operational fluid for powering a turbine in an 
aircraft will not fall below a preselected level even if the flow of fuel 
through a filter is restricted. 
This invention provides a fuel system with a bypass valve having an 
indicator which is actuated by initial movement of a piston responding to 
a predetermined pressure differential that develops between fuel that is 
presented to a filter and fuel that passes through the filter to inform a 
maintenance person that unfiltered fuel has entered the fuel system.

In the fuel system 10 shown in FIG. 1, fuel from a source or reservoir 12 
is supplied to a regulator 14, of the type disclosed in U.S. Pat. No. 
4,245,462, by a pump 16. The regulator 14, in response to an operational 
input from a computer 18, allows fuel from the pump to be communicated to 
the combustion chamber 20 in a turbine engine 22. The fuel that is 
supplied to the combustion chamber 20 is ignited and provides the force 
for rotating a turbine 24 within the engine 22 to create power which moves 
an aircraft. 
Operational parameters in the engine 22 are communicated to the computer 18 
which can provide the regulator 14 with a modifying signal to optimize the 
ratio of fuel to air supplied to the combustion chambers 20. A portion of 
the fuel supplied to the regulator 14 is diverted to operate the metering 
valve, governor, regulator and various other components in the regulator 
14 with any excess fuel being returned to reservoir 12 by return conduit 
25. 
In order that the components in the regulator 14 and injectors in the 
combustion chamber 20 operate in an acceptable manner over an extended 
period of time it is imperative that clean fuel be provided by the fuel 
system 10. As a result a filter 26 is located in supply conduit 28 to 
remove wax, dirt, water and other contaminates from the fuel prior to the 
fuel being supplied to the regulator 14. Unfortunately, when the filter 
removes contaminates from the fuel supply, the fluid pressure P.sub.s is 
reduced to a level P.sub.f for the fuel actually supplied to the regulator 
14. As long as the fluid pressure P.sub.f is above a predetermined value 
or level, the fluid regulator 14 operates in a satisfactory manner without 
any adverse effect on either the operation of the components or the actual 
fuel supplied to the injectors in the combustion chamber 20. 
A sensor in the regulator 14 is designed to provide a feedback to the CPU 
18 with respect to the fluid pressure P.sub.f in the fuel activity 
presented to the regulator 14. When the fluid pressure P.sub.f reaches a 
predetermined level which would effect the operation of either the engine 
22 or regulator 14 a warning signal is provided to the operator which 
indicates that filter 26 needs to be serviced. As long as the engine is on 
the ground, this single signal with respect to filter maintenance is 
adequate. However, if this signal develops when the aircraft is in flight, 
it is better that unfiltered fuel be supplied to the regulator 14 rather 
than the fluid pressure in the fuel be allowed to fall below a preselected 
value. Bypass valve 30 is designed to so assure that the fluid pressure 
P.sub.f of the fuel supplied to a regulator 14 from pump 16 is always 
above a minimal fluid pressure during operation of pump 16. 
Bypass valve 30 has a housing 32 with a chamber 38. Chamber 38 has an 
entrance port 34 and an exit port 36. Entrance port 34 is connected to 
pump 16 by conduit 40 while exit port 36 is connected to the output 
conduit of filter 26 or regulator 14 by conduit 42. Chamber 38 in housing 
32 is closed by an end cap 44 which has a cylindrical sleeve 46 that 
extends into chamber 38. Sleeve 46 has a series of radial openings 48 and 
51 that are aligned with a groove 52 in housing 32 associated with exit 
port 36. When flange 50 on end cap 44 engages housing 32, seals 54 and 56 
effectively seal chamber 38 from the surrounding environment. Bolt 94 is 
screwed into housing 32 to fix a retainer 90 such that end cap 44 can not 
be removed from housing 32 of bypass valve 10. A piston 58 located in 
sleeve 46 has a wall 60 with a projection 62 extending therefrom toward 
the entrance port 34. A spring 64 located between cap 44 and wall 60 urges 
face 66 toward a retainer stop 68. Thus, piston 58 is effectively caged 
within the cylindrical sleeve 46 of the end cap 44. A series of radial 
opening 70 and 72 on piston 58 allow the fluid pressure present in groove 
52 and exit port 36 to be communicated to the interior 88 of sleeve 46. 
An indicator member 74 has a cylindrical body 76 located in housing 32. 
Cylindrical body 76 has an end 78 that extends into chamber 38 and a first 
retainer groove 80 separated from a second retainer groove 82 by a land 
84. End 47 on sleeve 46 extends into grove 82 while end 63 on projection 
62 extends into groove 80. End 63 of projection 62 engages the cylindrical 
body 76 to hold face 75 flush with housing 32. 
As long as the fluid pressure P.sub.f of the fuel supplied to regulator 14 
is above a predetermined level, the force produced by the pressure 
differential created from the fluid pressure P.sub.s in chamber 38 and 
P.sub.f in chamber 88 can not overcome the force of spring 64 and piston 
58 remains on retainer stop 68 to prevent the flow of fuel from the 
entrance port 34 to the exit port 36 through chamber 38. 
When the pressure differential across wall 60 reaches a predetermined level 
corresponding to a pressure drop across filter 26, spring 46 is overcome 
and piston 58 moves away from retainer stop 68 to allow fuel to flow from 
entrance port 34 to exit port 36 through chamber 38 as illustrated by the 
position of piston 58 in FIG. 3. Flow of fuel through chamber 38 is 
essentially free of turbulence and contours 83, 85 and 86 (see FIG. 2) on 
projection 62 of piston 58 prevent retainer stop 66 from being moved from 
a groove in sleeve 46. When projection 63 moves out of the first retaining 
groove 80, the fluid Pressure P.sub.s acts on cylindrical member 76 and 
moves face 75 away from housing 32 to provide a visual indication that 
piston 58 has moved. Land 84 engages end 47 on sleeve 46 to prevent or 
limit the movement of face 75 with respect to housing 32. Flow from pump 
16 continues to bypass filter 16 until the demand for fuel to the engine 
22 terminates. 
When the demand for fuel for the engine 22 terminates, spring 64 moves 
piston 58 toward retainer stop 68 to again bring face 66 into engagement 
with retainer stop 68, as shown in FIG. 4, to prevent fluid flow through 
chamber 38. However, end 63 on projection 62 acts on end 78 of the 
cylindrical body 76 to prevent face 75 from re-entering housing 32. 
Indicator 74 thereafter remains unactivated until manually reset by a 
ground maintenance person through a process illustrated by the structure 
in FIG. 5. 
To manually reset the indicator 74, end cap 44 is screwed from housing 32 
until flange 50 engages shoulder 92 on retainer 90. When flange 50 engages 
shoulder 92, end 63 on projection 62 of piston 58 and end 47 on sleeve 46 
are aligned with the edge 31 of opening 33. Thereafter, cylindrical body 
76 of indicator 74 can be moved into chamber 38 until face 75 engages 
housing 32. Thereafter, end cap 44 is screwed into housing 32 until flange 
50 engages housing 32 to again align the structural components in a manner 
illustrated in FIG. 1. 
As clearly illustrated in FIG. 1, the bypass valve 30 is remotely 
positioned within the fuel system 10 with respect to the filter 26. In 
this remote position, during bypass flow particles or contamination is not 
removed from the filter element and introduced into the fuel system. In 
addition, maintenance and inspection by a flight crew.