Dispensing valve with tubular seal

A seal for a longitudinally movable element such as a needle valve. The seal has an upper disc-like portion which is secured in place and a lower tubular extension. The tubular extension has an internal tapered bore such that the lower end of the bore is narrower than the upper end of the bore. The lower end of the bore intimately grips the outer surface of the longitudinally movable element and stretches and retracts with its movement.

The present invention relates to an improved seal, and in particular to a 
seal for use with an elongate member which is slidable into and out of a 
space in which a liquid is to be contained. One example of such a 
situation is that of a needle valve controlling the discharge of a liquid 
from within a chamber where the needle valve extends through the chamber 
from one side to the other. 
In the past adequate sealing has been achieved, particularly in the case of 
a longitudinally movable elon gate member, using a diaphragm seal where 
the diaphragm extends between the periphery of the elongate member and a 
surrounding housing. Such a situation is illustrated in FIG. 1 from which 
it can be seen that the space 1 under the diaphgram 2 will vary in volume 
considerably as the elongate member (needle valve member 3) to be sealed 
is longitudinally displaced in a vertical direction. In the case of 
controlled dispensing of a liquid from within the space 1 through a nozzle 
4, the pressure within the space 1 will fluctuate giving undesirable 
fluctuations in the rate of discharge of the liquid introduced along the 
direction of arrow 5. 
An alternative form of seal which has not been subject to this fluctuation 
in the volume of the space 1 is the stuffing box seal, in this case a 
chevron shaft seal, shown at 2a in FIG. 2 which is another prior art 
arrangement. However, the fact that the needle valve member 3 slides 
relative to the chevron seals of the assembly 2a causes wear in the seals 
with the result that some of the liquid which has been introduced at 5 
into the space 1 can escape vertically upwardly and, particularly in the 
case of liquids which may be shear-sensitive there is a risk of 
agglomeration of the material at the seal, with undesirable consequences. 
It is an object of the present invention to provide a seal about a movable 
longitudinal member, which does not depend on sliding of the longitudinal 
member relative to the seal and equally does not involve the use of a 
membrane or diaphragm which flexes to vary the volume of the space around 
the elongate member. 
According to the present invention there is provided a seal for an elongate 
member movable longitudinally relative to a housing, comprising an 
elongate annular seal member having an internal bore therealong, and means 
for clamping a first end of the elongate annular seal member relative to 
said housing, the elongate section having a distal end remote from the 
clamped end, arranged to contact the exterior of the longitudinally 
movable valve with the wall of said bore in the elongate annular seal 
member. 
A preferred form of the present invention is a dispensing gun for a liquid 
composition, comprising a dispensing chamber for the liquid composition 
and a needle valve projecting across the chamber to close off a discharge 
orifice of the chamber from within the chamber, the point of entry of the 
needle valve member into the chamber being sealed by means of a seal in 
accordance with the present invention.

Referring now to FIG. 3 which embodies the present invention, the seal 2b 
in this case comprises a long tubular extension 11 joined to a disc-like 
portion 12 which in turn is joined at 13 to an annular locating skirt 14. 
The seal 11, 12 is held within the dispenser body 22 of a dispensing gun 
for the liquid, by virtue of the disc-like portion 12 being clamped 
between a male seal clamping body 17 and a female clamping ring 18. The 
body 17 and ring 18 are held within the fixed housing of the dispenser 
body 22. An annular projection 16 of the male seal clamping body 17 
locally compresses the upper surface of the disc-like portion 12 to 
increase the sealing pressure between the male seal clamping portion 17 
and the disc-like seal portion 12. 
In order to locate the seal in place, the male clamping body 17 fits into a 
recess of the female seal clamping ring 18 so as to trap the disc-like 
portion 12 and the locating skirt 14 of the seal 2b in place. 
The housing of the dispenser has an inlet at 20 and is completed by a 
nozzle body 19 having a nozzle orifice 21 to be closed by the tip 3a of 
the longitudinally movable elongate needle valve member 3. 
Once a liquid under pressure for dispensing through the nozzle orifice 21, 
has been introduced into the liquid-receiving space 1 its pressure will 
hold the lower end of the elongate sleeve portion 11 of the seal in 
contact with the cylindrical exterior of the longitudinally movable needle 
valve member 3. The elongate extension 11 is deliberately given an 
internal taper such that its interior is more likely to contact the needle 
valve member 3 near the lower end or tip of the extension 11 than it is 
higher up the needle valve member 3, thereby allowing some degree of 
longitudinal movement of the needle valve member 3 relative to the upper 
parts of the extension 11. 
In use, the lower end of the extension 11 will intimately grip the exterior 
of the needle valve member 3 so that when the needle valve is moved 
downwardly the extension 11 will be stretched axially as the needle valve 
member 3 moves longitudinally within the interior of the extension 11. 
During this time the disc-like portion 12 and the locating skirt 14, being 
held in place by engagement of the male clamping body 17 and female seal 
clamping ring 18, ensure that the upper end of the extension 11 is held 
stationary relative to the axially movable lower end, giving rise to 
expansion and contraction of the extension 11. It should of course be 
appreciated that as the extension 11 expands and contracts longitudinally 
there will be a change in its external cross-section which will be in the 
form of a decrease when the length of the extension 11 is becoming larger, 
and vice versa. 
It should also be noted that there is substantially no sliding of the 
interior wall surface of the extension 11 relative to the needle valve 
member 3 which it encloses, and thus there will be no wear of the fit of 
the seal in repeated use of the needle valve. 
The needle valve may be operated by any suitable drive mechanism, for 
example by mechanical means, electrical means, pneumatic means, or 
hydraulic means, or a combination thereof. 
Any suitable natural or synthetic elastomeric material may be used for the 
seal member 2b, and one example is neoprene; another is natural rubber. 
As indicated above, there are serious disadvantages in the use of the 
diaphragm seal shown in FIG. 1 or the stuffing box "chevron" type of seal 
shown in FIG. 2. With the FIG. 1 arrangement the diaphragm displaces 
vertically in such a way as to change the volume of the chamber 1 so that 
the pressure of the liquid in the chamber will also fluctuate and will 
give rise to undesirable changes in the rate of discharge through the 
nozzle orifice. 
Experiments have proven that the present seal provides a better performance 
than the diaphragm with respect to the evenness of compound distribution 
on the can end. The results of these experiments are set out in Table 1 
below showing typical peripheral weight distribution (mg) around a gasket 
lined with a nominal 2.2 turn lining. This means that the can end turned 
through a nominal 2.2 turns while the needle valve of the gun above it was 
open. Thus there was an area of a nominal 0.2 turns on which three layers 
of compound fell in place of the two layers everywhere else. The overlap 
area is contained in Octants 1 and 8 of Octants Nos. 1 to 8 given in Table 
1. The weights quoted for the remaining Octants 2 to 7, and the average 
and standard deviation values for that set of Octants quoted in Table 1 
illustrate the superiority of the present seal. 
TABLE I 
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Diaphragm 
Present Seal 
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1 13.4 11.1 
2 11.1 7.7 
3 5.6 7.7 
4 6.8 7.6 
5 7.4 7.9 
6 9.2 7.9 
7 9.4 7.7 
8 10.6 9.2 
Av. 8.25 7.75 
St Dev. (2-7) 2.01 0.12. 
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In fact the average for the full can end over Octants 1 to 8 was 9.2 using 
the diaphragm seal and 8.4 using the gaiter seal in accordance with the 
invention, and the standard deviation was 2.5 using the diaphragm seal and 
1.2 using the present seal. Even over this range, which includes the 
unfavourable "overlap area" of Octants 1 and 8, there is a distinct 
improvement using the present seal in accordance with the invention. 
The reason for this improvement using the present seal of FIG. 3 is thought 
to be that, in the diaphragm seal gun, as the needle valve 3 rises to open 
the nozzle orifice the pressure in the chamber 1 drops and hence the rate 
of discharge of the liquid composition from within the chamber 1 will drop 
until it can be restored as a result of the pressure recouperation of the 
continued feed into the chamber at 5. A further disadvantage is that even 
while the needle valve 3 is stationary the diaphragm is able to displace, 
for example by a fluttering movement when the valve is open, and thus the 
pressure varies undesirably. 
An additional advantage of the present seal over the stuffing box seal when 
used with a gun operated independently of the machine, i.e. air operated 
via a solenoid, is that there is reduced friction between the needle and 
the flange seal area which provides for a more consistent operation. 
With the FIG. 2 arrangement there is no such variation in volume of the 
chamber 1 but the sliding of the needle valve member 3 relative to the 
stuffing box seal assembly 2a will give rise to wear of the sliding fit 
and eventual leakage of liquid composition upwardly along the needle valve 
with a risk of contamination of the drive mechanism for the needle valve 
member 3. Furthermore, the high shear generated around the needle valve 
member 3 at the stuffing box assembly 2a and at the orifice of the 
surrounding part of the stuffing box support member 6 of FIG. 2, has been 
found to give rise to coagulation of the liquid composition being 
dispensed, particularly in the case of shear-sensitive compositions, such 
as water based dispersions, with the risk of coagulated particles of the 
composition being formed which may partially block the nozzle orifice 21 
so as to reduce the rate of discharge of the contents of the chamber 1 or 
even completely block it. One example of a liquid composition which may be 
coagulated by the high shear forces generated in a seal of this type is a 
water based can sealing compound which may comprise an aqueous 
styrene-butadiene rubber latex, tackifying resin, filler, dispersant and 
thickening agent. 
With the seal illustrated in FIG. 3, constructed in accordance with the 
present invention, no such change of volume disadvantage of FIG. 1 is 
noticed and equally there is substantially no risk of coagulation of the 
liquid composition or of contamination of the needle valve member drive 
mechanism through escape of liquid composition from the chamber 1 upwardly 
along the needle valve member 3. 
When dispensing water based sealing compound for can lining, using a seal 
in accordance with the present invention, it has been found in preliminary 
tests that there are minimal pressure surges in the compound, to the 
extent that no problem arises, and nevertheless adequate seal is provided 
without any noticeable incidence of coagulation of the compound. 
While this invention has been described with reference to its preferred 
embodiments, other embodiments can achieve the same result. Variations and 
modifications of the present invention will be obvious to those skilled in 
the art and it is intended to cover in the appended claims all such 
modifications and equivalents as fall within the true spirit and scope of 
this invention.