Piston pump with rolling membrane

A piston pump having a flexible rolling membrane which seals the piston from the cylinder wherein the piston is designed to include an upper portion which is spaced inwardly from the cylinder wall so as to form a cavity which communicates through channels and seals carried by the lower portion of the piston in such a manner that the lower portion of the flexible membrane is depressed between the upper portion of the piston face and the cylinder walls during an intake stroke as the cavity is subjected to a decreased pressure and which decreased pressure is removed from the membrane during a discharge stroke of the piston. In the preferred embodiment, the membrane is secured to the upper surface of the piston by a cup-shaped element which protects the membrane from materials within the cylinder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improvements made to piston pumps of which the 
seal between the piston and the cylinder bore consists of an rolling 
membrane. 
2. Histroy of the Related Art 
This membrane type of seals for piston pumps is known to allow for a longer 
piston stroke and perfect sealing. Unfortunately, it is practically 
impossible to use such an rolling membrane on sucking and forcing pumps 
due to the depression resulting from the sucking phase. The piston motion 
causes partial vacuum inside the cylinder, so that the membrane does not 
keep flat against the piston periphery, starts folding inside the cylinder 
and wears out very quickly. 
Objects of the Invention 
The object of the improvements covered by this invention consists in 
creating the conditions required for the use of rolling membranes as seals 
for suction and forcing pumps. 
For this purpose and according to the invention, the piston is designed to 
create a depression behind the membrane during the suction phase, in such 
a way that the membrane can unroll without parting from the piston skirt. 
The piston's design also serves to cancel this depression during the 
forcing phase. 
According to a particularly interesting arrangement, the piston skirt of 
the pump according to the invention presents at the top of the piston a 
first part the diameter of which is significantly smaller than the 
cylinder bore, and then a second part of which the diameter is equal to 
the cylinder bore except for the working clearance between both elements. 
A peripheral groove is machined in the second part of the piston skirt, 
close to its junction with the first part, and an axial groove runs from 
the first groove and ends into the base of the second part. The width of 
the groove being larger than the diameter of the common type O-ring 
engaged in the peripheral groove and intended to achieve sealing between 
the piston and the cylinder during the suction phase, in order to create a 
depression between the joint area and the membrane, or, on the contrary, 
in order to release the sealing during the forcing phase.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The suction and forcing or discharge pump according to the invention 
represented on the drawings consists mainly of a cylinder 1 made of a 
lower part 2 and of an upper part 3, of a piston 4 and of an rolling 
membrane 5 of which the upper part of the side wall is clamped between the 
parts 2 and 3 of the cylinder 1, while the bottom thereof works in 
association with the top of piston 4. 
Of course the piston moves reciprocatingly inside the cylinder bore 1 and 
is driven by means of a connecting rod 6 attached to the crank pin 7 of a 
crankshaft, the circular movement of said crank pin being represented by a 
dot and dash line. The upper end of the connecting rod is articulated onto 
piston 4 by means of a pin 8 engaged in a fork joint 9a protruding out of 
the internal face of the top part 9 of the piston. 
The skirt of the piston 4 comprises a first part 10 of which the diameter 
is significantly smaller than the cylinder bore, and a second part 11 
located under the first one and having a diameter approximately equal to 
that of said cylinder bore, except for the working clearance between both 
elements. 
The lower part 11 of the skirt of piston 4 is provided, close to its 
junction with the upper part 10, with a peripheral groove 12 whose width 
and depth are larger than the common type O-ring 13 engaged in the groove. 
This results in some side and axial clearance between the ring seal and 
the groove's walls. A longitudinal groove 14 extends from the groove 12 
and provides for communication between the lower part of the piston skirt 
and said peripheral groove. 
As can be seen, the bottom of membrane 5 is associated with the top 9 of 
piston 4 by means of a cup 15 attached to the piston top by a threaded pin 
and nut device 16-16a. By this arrangement, the bottom of the membrane is 
clamped between said cup and the top 9 of piston 4. The cup's base 
protrudes beyond the external face of piston 4 so as to orient the 
junction area between the piston side wall and the membrane bottom 
slightly towards the bottom of the space included between the upper part 
10 of the piston and the bore of cylinder 1. The cup 15 is provided with a 
peripheral wall 15a which extends above the cup's base and whose 
peripheral face is in form of a truncated cone opening downwards. 
The bore of the lower part 2 of cylinder 1 is cylindrical, while that of 
the upper part 3 is slightly tapered and opening downwards in the same way 
as the peripheral face of the wall 15a of cup 15, with substantially the 
same conicity. 
It can be seen that the upper part 3 of cylinder 1 is closed by a cross 
partition 3a, which is equipped with two valves 17, 18 intended to 
obturate the ports 19, 20 respectively. The valve 17 and the ports 19 
communicate with the chamber 21 into which the liquid is aspirated, while 
the valve 18 and the ports 20 are associated with the discharge chamber 
22. 
In a preferred form, the bore of the lower part 2 of the cylinder can be 
fitted with two ribs 2a engaging into the grooves 14. This co-operation 
makes it possible on the one hand to guide the piston properly with 
respect to the cylinder, in order to prevent the membrane from twisting, 
and on the other hand to clean the grooves and to ensure free and steady 
passage of air. 
The pump operates as follows: 
In the discharge phase (see FIG. 2), the piston 4 moves upwards in the 
direction of the F1 arrows. The pressure inside the chamber 23 as defined 
between the piston and the bore of cylinder 1 pushes the side wall of 
membrane 5 both against the bore and against the peripheral face of part 
10 of piston 4. The valve 17 is then closed, of course, while valve 18 is 
open in order to let the previously aspirated liquid flow out towards 
chamber 22 through the ports 20. During the upward movement of the piston, 
the O-ring 13 is pushed against the lower face of the groove 12 (FIG. 3) 
as a result of its friction contact with the lower part 2 of cylinder 1. 
This lower part communicates through the groove 14 with the space 24 as 
defined respectively by the bore of the part 2 of the cylinder 1, the 
peripheral face of the part 10 of the piston 4, the shoulder 25 formed by 
the parts 10 and 11 of the piston and the membrane 5. So, when the piston 
moves upwards, said space 24 lies under atmospheric pressure. 
When the piston reaches its top dead center, the side face of the wall 15a 
of the cup 15 comes in contact with the top end of the tapered bore of the 
upper part 3 of cylinder 1, so that, when the pump is at rest in that 
position of the piston, the membrane is fully protected from the liquid 
contained in the discharge chamber 22 or in the aspiration chamber 21. In 
particular, the particles in suspension concentrate by decantation in the 
hollow part of the cup 15 as defined by its partition 15a. 
When the linear displacement of the piston 4 reverses, i.e. when the piston 
passes over its top dead center, the valve 18 closes and the valve 17 
opens, which starts the aspiration stroke. The downward movement of the 
piston causes its groove 12 to slide with respect to the seal 13, which 
remains stationery (see FIG. 4), so that it interacts with the lower face 
of shoulder 25 (FIG. 5). It is easy to understand that a partial vacuum is 
created inside the space 24 as the piston moves further down, so that the 
membrane is aspirated into this space without possibility of folding on 
the top of the piston. 
In this way, the membrane unrolls properly until the piston 4 reaches its 
bottom dead center. The seal 13 remains in the same position (FIG. 5). As 
soon as the piston passes over its bottom dead center, the pump reverts to 
the position of FIG. 3 after the groove 12 has changed its position with 
respect to the seal 13, which remains stationery (FIG. 4), in order to 
bring the space 24 back under atmospheric pressure and to provide for a 
proper rolling of the membrane without any risk of damage to same. 
At last, it should be noted that the displacement of the piston 4 between 
its bottom and top dead centers is such that its lower part 11 interacts 
only with the cylindrical bore of the lower part 2 of cylinder 1. 
If the pump remains at rest with the piston at bottom dead center (FIG. 1), 
the major part of the particles in suspension in the aspiration and/or 
discharge chamber(s) and in the space 23 are collected into the cup 15, 
where they don't endanger the membrane 5. 
It is to be understood that the foregoing description is given only as an 
example and that it doesn't restrict in any way the scope of the 
invention, which would still apply in case realization details were to be 
modified or replaced by any other equivalent ones.