RECOMMENDATIONS FOR A RADICAL RE-DESIGN OF THE PNEUMATIC VALVE TO REDUCE THE NUMBER OF PARTS IN THE ASSEMBLY
The following design changes are recommended to reduce the cost of the assembly of the pneumatic valve :
(1) Eliminate the choke screw housing (6) by providing an internal
thread in the valve body, where the choke screw housing sub-assembly is
currently situated. This would involve the use of a choke screw
and O-ring only, thus eliminating two parts. .
(2) Eliminate the gasket (2) and top cover (23) by moulding the airway
into the integral body and top cover. This would eliminate two parts
but would require the bodies to be stocked in two styles to accommodate
single acting and double acting valves.
(3) Eliminate the piston sleeve (9) by reducing the bore of the body at
this point so that the piston is guided by the body, instead of the
(4) Eliminate the three sleeves (9), (12), (14) and integrally mould the three sleeves as one part.
(5) Eliminate the piston by integrally moulding it with the spool piece, for single acting valves.
(6) Eliminate the spool piece O-rings / sealing rings and locate them on the spool piece sleeves.
(7) Eliminate one end piece and integrate it with the valve body.
(8) Eliminate the indicator and integrate it with the spool piece.
(9) Eliminate the label and print it directly onto the valve.
(10) Eliminate the cover screws and incorporate (a) a bayonet fitting or, (b) a screw thread between the body and end cover.
(11) Eliminate the short spring by changing the following design features of the long springs :
(a) spring wire gauge
(b) number of turns per inch
(c) spring material
(d) external diameter of spring
CONSIDERATIONS FOR THE RE-DESIGN OF THE PNEUMATIC VALVE
There are many factors that must be considered when re-designing the
pneumatic valve for assembly. The effect of changing one design
feature of a part may have an effect on the design of the other
parts. The performance of the valve can be reduced by adverse
design changes, or there may be an increase in the manufacturing costs
of the product parts, due to new tooling costs. A number of
factors must be considered when the re-designed valve is being
(1) A capital investment has been made by the client company in mould
tooling for the valve body. If other part features are to be
integrated within the body, or if the body is to be split into more
than one component, then there will be an investment required for the
new mould tooling.
(2) If the choke screw housing feature is to be integrated within the
valve body then the body tooling modification cost, and the scrapped
choke screw housing tooling cost, must be considered.
(3) The assembly of the O-ring seals to the spool piece presents the
problem of expanding the O-rings over the part and then allowing them
to contract into the o-ring groove. The task can be simplified by
re-designing the joints between the spool piece sleeves.
Unfortunately, the current design of joints has been carefully chosen
to avoid the possibility of an O-ring passing over a joint between two
sleeves. It would be very difficult to achieve this same
performance, so that the valve would operate for more than 3 000 000
cycles without a loss in performance.
(4) The spool piece is surrounded by sleeves having a multitude of
holes in them. It would be logical to eliminate the sleeves and
to direct the flow of air from one port directly to another port.
However, these sleeves are required to provide an even flow path around
the spool piece to maintain the required flow rate. Larger ports
could be moulded into the valve body, but this could cause the
O-rings to be damaged as they passed over the ports.
(5) The piston is guided by the piston sleeve. This piston guide
design feature could be integrated within the valve body. The
inside diameter of the piston guide must be such that the air pressure
required to operate the valve is no greater than that already
required. Additionally, it must still be possible to insert
internal parts to the valve body. If the piston sleeve is
integrated into one half of the body only, for spring return valves,
then all of the parts associated with the spool piece can be inserted
from one end of the of the valve. This option would, of course,
require there to be two valve bodies for the product range.
(6) The thrust from a new single spring must be such that it can
overcome the action of the fluid pressure and the friction between the
spool piece O-rings and the sleeves.
(7) The sleeves are moulded as separate components because, as an
integral part, it would be difficult to get the correct distribution of
plastic in the mould. If the sleeve must be split for this reason
then it would be advantageous to situate spool piece O-ring seals
between the sleeves.
(8) It must be impossible to inadvertently unscrew the choke screw out
of the body. If the valve was to be re-designed so that the choke
screw could be inserted into the body after assembly of the cover, or
into a body with an integral top cover, difficulties may arise.
If the choke screw can be inserted after the cover, or cover feature,
then it could also be removed by screwing. The addition of a
retaining part would be counter-productive and, therefore, a stamping
operation would be more efficient. The tops of the choke screw
holes would be deformed after insertion of the choke screw, thus
(9) During manual assembly of the spool piece sub-assembly to the valve
body, special tools are required to assist the operator. The
outside diameter of the sealing ring is much larger than the inside
diameter of the spool piece sleeve. A special tool is required to
contract the rings before insertion into the valve body. The
operation is so complex that it may not be efficient to carry it out by
a robot, in its current state of design.
(10) The operation of inserting the spool piece sub-assembly into the
valve body is so complex that it is not feasible for it to be done by
(11) The piston and lip seal can only be inserted into the sleeve in
one direction. This is because the lip of the seal has a larger
diameter than the inside of the sleeve. The piston could be
inserted in both directions if the seal was an O-ring.
(12) If one of the end pieces were to be integrally moulded with the
body then all parts could only be inserted into the body from one
direction. The sealing of the indicator would create special
problems. If the seal is inserted by the robot then it cannot be
sufficiently located. Otherwise, the robot would not be able to
assemble the seal. During movement of the indicator, the seal may
be removed from its housing.
(13) Integration of the top cover would make it impossible to change
the routing of the signal air because the gasket would no longer be
(14) The current pneumatic valve design currently has two springs to generate the required thrust.
(15) The pin is required for the stability of the long spring, during operation.
(16) For aesthetics, the top cover and end covers must be of aluminium, to give the impression of robustness to the product.
(17) The dimensions of the inlet / outlet ports must be kept the same
for compatibility with complimentary and substituted products.