Piston and valve arrangement

The invention relates to a piston for a quick dump valve disposed for filling a space after the evacuating or dumping of that space. The piston is in the form of a plate (21) having a short peripheral flange (22), the external face of which assures only relative guidance by engaging the cylinder with a play sufficiently great as to reserve a passage (3) for the gas supplied via the feed opening sufficient to allow this gas to reach the space and a medial flange (23), the edge of which has a bearing surface the shape of which is complementary to that of the seat (9) with which it cooperates in order to close the discharge passage. The valve is particularly adapted for improving the outflow of products at the outlet of silos.

The invention relates to a quick-dump valve and also to a valve piston for 
effecting pressurization of a space after the quick evacuation or dumping 
of that space. 
The invention is applicable particularly, but not exclusively, to improving 
the outflow of a granular or pulverized product at the outlet of equipment 
such as silos or hoppers. The invention assures this improvement in 
outflow by eliminating stagnant packets in dead zones and/or by destroying 
either the material layer normally adhering to the wall or the bridge or 
arch formed by the product before the orifice of the outlet. 
A quick-dump valve of this kind, sometimes called an air cannon, includes, 
on the one hand, a feed chamber provided with a refill opening and an 
opening communicating with the space to be pressurized and, on the other 
hand, a discharge passage to the equipment in which the sudden-discharge 
valve is applied. The feed chamber is embodied at the rear of a cylinder 
in which a freely translating piston is disposed. The piston undergoes a 
thrust in one direction due to the effect of a pressure, particularly that 
of the gas introduced into the feed chamber in order to refill the space. 
In order to monitor the circulation of the gas in the discharge passage, 
this passage is divided into two sections by a seat with which a closure 
means cooperates. The closure means supports or directly embodies the 
piston. Seating of the piston is assured by the pressure acting upon the 
piston. As soon as the corresponding pressure is relieved in the feed 
chamber, the pressure of the gas located in the space acts upon the piston 
in the opposite direction from that of the thrust mentioned above and 
causes a rapid return stroke of the piston, which violently opens the 
discharge sleeve of the space, until the feed pressure reappears in order 
to refill or pressurize the space once again. 
For the sake of slackening this feed pressure, the refill opening is 
generally connected to a source of gas under pressure via a 
multi-directional control valve, in particular making it possible 
arbitrarily either to close this opening or connect it to the pressure 
source or to the ambient air. 
Aside from the fact that valve structures of this type are complicated and 
hence quite expensive, the first valves of this type to appear on the 
market are believed to be disclosed in U.S. Pat. No. 3,942,684 and have 
various disadvantages. A major disadvantage is the loss of pressure or 
head undergone by the gas when, because of the seat of the closure means, 
the gas has to traverse a passage of relatively narrow cross section in 
order to effect the discharge. The gas then takes more time to flow out, 
and this in turn considerably reduces the suddenness of the discharge. 
Another disadvantage of this type of valve is due to the weight and hence 
the inertia of the piston and also to the bulk of the piston and its 
chamber. This is due to the fact that the piston had to be long enough, 
its length being in particular greater than its diameter, to assure that 
is guided as accurately as necessary in the cylinder in order to avoid any 
seizing, despite the fact that its fit in the interior of the cylinder is 
practically without play in order to establish the tightness between the 
feed chamber and the front of the piston necessary to guarantee the return 
of the closure means to its seat. 
More recently, a new quick-dump valve intended to overcome the first of 
these disadvantages and hence to prevent a loss of head has appeared and 
is disclosed in French Pat. No. 2.429.952. The new valve of this French 
patent maintains a discharge passage of practically constant cross 
section, even through the seat. In this valve, the cylinder has a length 
equal to at least twice the diameter of the discharge passage, one of the 
sections of which is connected with the front of the cylinder, while the 
other section is pricked radially and toward the front of the cylinder in 
such a manner that its opening communicating with the cylinder is closed 
by the piston when the piston is at the front, but is opened widely when 
the piston is at the rear. The opening communicating with the cylinder 
then directly embodies the seat of the closure means, which is formed by 
the lateral surface of the piston. 
For the sake of its guidance, as mentioned above, but also to embody the 
closure means of this seat, the piston must always have a length greater 
than the diameter of the discharge opening, resulting in both a piston and 
a cylinder that are long and therefore heavy, and hence causing the piston 
to have a certain inertia and a control requiring a large passage. This 
results in increased costs for materials for, and increased bulk of, both 
the piston and the cylinder. 
Because of this weight, at least one of the ends of the piston is equipped 
with a stop of relatively flexible material in order to limit the damage 
caused by the impacts of the piston at the end of its stroke; 
unfortunately, however, this material, deteriorates rapidly. Further, this 
material generally prevents its usage in systems operating at high 
temperatures. High temperatures heat the valve by conduction to the point 
that the stop deteriorates. This is the case, for example, in cement 
works. 
One object of the invention is to provide a quick-dump discharge valve 
piston which, while avoiding the loss of head and any seizing of the 
piston, is slight in length and hence has reduced weight, inertia and 
bulk. These and other advantages of the subject invention are obtained in 
a piston of the above type characterized in that it is in the form of a 
plate provided, first, with a short peripheral flange, the external face 
of which assures only relative guidance by engaging the cylinder with a 
play sufficiently great as to reserve a passage for the gas supplied via 
the feed opening sufficient to allow this gas to reach the space and, 
second, with a medial flange the edge of which has a bearing surface the 
shape of which is complementary to that of the seat with which it 
cooperates in order to close the discharge passage. 
Another object of the invention is to provide a quick-dump valve provided 
with such a piston.

Referring to the drawings, the valve includes: a feed chamber 1 provided 
with a refill opening 2 and passages 3 and 5 leading to a space 4. The 
discharge passage is shown in two sections 5, 6 connected to the equipment 
7 to which the valve is connected. 
A free piston 8 is disposed in the feed chamber 1 and undergoes a thrust in 
the direction of the arrow F due to the effect of the pressure of the gas 
introduced into the chamber 1 in order to refill or pressurize the space 
4. In order to monitor the circulation of the gas in the discharge passage 
comprising sections 5, 6, this passage takes its course by way of a seat 9 
cooperating with a closure means embodied directly by the piston 8. The 
first section 5 of the discharge passage extends from the space 4 to the 
seat 9, while the second section 6 of this discharge passage extends from 
the seat 9 to the equipment 7 and forms the discharge sleeve per se. The 
seating of the closure means is assured automatically as a result of the 
above-mentioned pressure pushing the piston 8. 
As soon as the feed pressure in the chamber 1 has slackened i.e., is 
reduced, the gas pressure prevailing in the space 4 like-wise acts upon 
the piston 8, but in the opposite direction from the arrow F, causing the 
piston to return with a rapid stroke. This piston 8 thus violently opens 
the seat 9 of the discharge sleeve 6. 
With a view to slackening or reducing the feed pressure in chamber 1, the 
refill opening 2 is connected to a source 10 of gas under pressure, via a 
conduit in two sections 11, 12 interconnected via a three-way valve 13 
allowing the closure of this opening 2 or its connection with either the 
pressure source 10 or the ambient air. 
The feed chamber 1 is formed by a housing defined by the piston 8 at the 
end of a cylinder 14, which at this end is for this purpose provided with 
a bottom or closure cap 15 traversed by the refill opening 2. This 
cylinder also includes, first, a connecting flange 16 connecting one (5) 
of the sections 5, 6 of the discharge passage with the space 4 and, 
second, a tubular element 17 limiting the displacement of the piston 8 
toward the front, while the inlet of element 17 embodies the seat 9 of the 
closure means 8. This tubular element 17 protects the other section 6 of 
the discharge passage and for this reason has at its outer end a flange 18 
connecting it with the equipment 7. 
This tubular element 17 penetrates the cylinder 14 on the one hand such as 
to reserve between it and the cylinder an annular conduit the cross 
section of which is equal to the inside cross section of the tubular 
element and thus to the cross section of the section 6 of the discharge 
passage which it protects and, on the other hand, at a depth such that 
after the return stroke of the piston a passage remains between the 
closure means 8 and the seat 9 at the periphery of the seat, this passage 
being in the form of a lateral surface of the cylinder, the length of 
which is equal to that of the distance across the tubular element 17 and 
thus to the distance across the cross section of the section 6 of the 
discharge passage which it protects. 
The other section 5 of the discharge passage is shown to be connected to 
space 4 via an opening 19 of the same cross section toward the front of 
the cylinder, for example by means of a conduit 20 perpendicular to the 
axis of the cylinder 14 and having a flange 16 connected to an associated 
flange of a conduit leading to or defining space 4. 
According to one characteristic of the invention, this conduit 20 is 
connected between the short 25 and long 26 bases of a truncated cone 27 
forming the lower end of the cylinder and by way of which the cylinder is 
connected on the periphery of the tubular element 17. This conicity is 
such as to assure the constancy of the cross section of the passage 
between the conduit 20 and the annular passage reserved between the 
tubular element 17 and the cylinder 14. 
According to one characteristic of the invention, the piston 8 is in the 
form of a plate 21, provided with a short peripheral flange 22, the 
external face of which assures only relative guidance by engaging the 
cylinder with a play sufficiently great so as to reserve a passage 3 
formed by the clearance between the outside diameter of plate 21 and 
diameter of cylinder 14 in the area of stroke of piston 8. As shown in 
FIG. 2, this area of the cylinder has a constant diameter due to the 
straight side wall of the cylinder at the top end of the cylinder 14 as 
shown in the drawing. The lower end of cylinder 14 takes the truncated 
cone form between the short 25 and long base 26 as previously described. 
Thus, passage 3 between the circumferential edge of plate 21 and cylinder 
assures that the gas supplied via the feed opening reaches the space 4 via 
conduit 20 and discharge passage 5. Piston 8 also includes a medial flange 
23, the edge of which has a bearing surface the shape of which is 
complementary to that of the seat 9 with which it cooperates in order to 
close the discharge passage. The peripheral flange 22 is sufficiently fine 
and short that in the discharge position it does not block the cross 
section of the passage. Plate 21 has a diameter slightly less than that of 
the cylinder. 
In a preferred embodiment, in order to assure self-centering, the seat 9 
and the bearing surface 24 of the medial flange are conical and the seat 
and bearing surface may be metal. Thus embodied, the piston makes it 
possible to assure a metal-to-metal seal allowing the use of the valve in 
equipment that operates at high temperature and/or in a corrosive 
atmosphere. 
All of the portion of the piston located at the periphery of the tubular 
element plainly has a surface that is amply sufficient to assure the 
instantaneous return of the piston to the bottom of the cylinder as soon 
as the feed pressure disappears. The baffle effect produced by the 
peripheral flange in turn prevents any escape of the discharging flow 
upward toward the feed chamber, the inlet or refill opening 2 of which is 
furthermore relatively closed by the application of the piston against the 
bottom 15 of the cylinder. 
Because of these simple short flanges, the piston is very light in weight 
and is not bulky, and only slight displacements are required in order to 
control it. Space 4 may represent the output or discharge opening of a 
silo the contents of which are discharged through equipment or discharge 
pipe 7 through the valve embodying piston 8 and the pressure applied to 
the surface of its plate 21 via feed or refill opening 2.