Syringe adapted to overcome a pressure resistance

A syringe is adapted to overcome a pressure resistance at its outlet as may be provided, for instance, by a filter in communication with the outlet and through which the syringe is to pump a medium, particularly a liquid medium, for filtration. The syringe comprises a first cylinder containing a piston and a piston rod. The piston rod is fixed to a second piston sliding within a longitudinal bore in the first-mentioned piston. The bore and the second piston cooperate to define an air-filled pressure chamber connected to a first cylinder chamber, defined by the first piston and the first cylinder, by a valve. Inward movement of the piston rod produces an over-pressure (e.g. 16 atmospheres) in the pressure chamber to open the valve to apply the over-pressure to the liquid or other medium in the cylinder chamber to overcome the pressure resistance of the filter and enable the liquid to be forced through the filter.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a syringe comprising a cylinder, a piston rod and 
a piston disposed for displacement within the cylinder by displacement of 
the piston rod, whereby when the piston rod is displaced in one direction 
a medium is drawn into the interior of the cylinder while when the rod is 
displaced in the opposite direction the medium is expelled from the 
cylinder. 
2. Description of the Prior Art 
Such syringes are used, for example, for forcing media through filters. In 
this case, a filter assembly disposed in a filter holder may be connected 
to the outlet of the syringe. Such arrangements are used, for example, for 
the cleaning or sterile filtration of small quantities of liquid. In 
order, then, to propel the liquid, for example in a quantity of 1 to 50 
ml, through the filter assembly which is connected to the syringe, a high 
pressure is required which has to be generated by hand. In the case of 
known syringes, the liquid or other medium to be filtered is forced 
through the filter assembly by an inward movement of the piston rod and 
thus an inward movement of the piston disposed in the cylinder. Under such 
circumstances, the hand must apply considerable force. In the case of very 
dense filter materials or where several filter materials are connected in 
series, particularly diaphragm filters, filtration in this manner is 
impossible. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a syringe with which it is 
possible to overcome pressure resistance as might be afforded by filter 
means. 
This object is achieved in that there is provided in the interior of a 
first piston in a first cylinder a pressure chamber having a cross section 
which is reduced in size with respect to the cylinder first cross section. 
Upon inward movement of the piston rod, an over-pressure is created in the 
pressure chamber. When there is an over-pressure, the pressure chamber can 
be connected to the cylinder chamber in which is disposed the medium which 
is to be expelled, the connection being made by a connecting device having 
shut-off means. The over-pressure forces the medium out of the syringe 
against any pressure resistance. 
The pressure chamber is disposed in the interior of the cylinder and the 
pressurizable medium disposed therein may be air. A simple construction is 
possible if the pressure chamber is constructed as a duct extending in the 
direction of displacement of the piston rod, the piston rod being guided 
in the duct. Furthermore, that end of the piston rod which is disposed in 
the interior of the first piston may be provided with a second piston 
which is displaceable in the duct and which forms one end of the pressure 
chamber, the connecting device with the shut-off means being disposed at 
the other end limit of the pressure chamber. 
This connecting device with the shut-off means can be a valve which is 
opened as a result of over-pressure in the pressure chamber. As a result, 
the over-pressure produced in the pressure chamber by the depression of 
the piston rod is applied to the medium to be expelled from and disposed 
in the cylinder chamber in front of the first piston. 
Furthermore, the second piston which is displaceable in the interior of the 
first piston can be provided with a valve. The piston rod can be 
alternately moved into and out of the second cylinder formed in the first 
piston, exerting a pumping action on the medium which is to be expelled, 
so that by reason of this pumping action, the medium can be forced through 
the filter arrangement or overcome some other pressure resistance. 
In order to guarantee a functionally-correct opening and closing of the 
valves, the valve closure elements can be biased by adjustable spring 
forces as is apparent to those skilled in the art. 
An important advantage of the invention resides particularly in the fact 
that it is possible, by applying a small amount of force, to overcome for 
example a high difference in pressure obtaining in a filter assembly. 
Thus, in the case of very dense filter materials or in the case of 
multiple filter materials disposed one after another, particularly 
diaphragm filters, a filtration operation can be performed which was not 
hitherto possible with a syringe. By repeated reciprocating movement of 
the piston rod and by reason of the pumping action exerted thereby on the 
medium to be expelled, it is possible to eliminate from the interior of 
the cylinder all the liquid which is to be filtered, the liquid being 
forced out through the filter arrangement. Also, it is possible by means 
of the invention to expel finely adjusted doseages from the cylinder. 
The device according to the invention is extremely versatile in 
application. For example, it can be used for the sterile filtration of 
pharmaceutical liquids such as for example eye drops or parenteral 
solutions. Furthermore, it can be used for example in homeopathic 
dispensing. The invention can also be used to advantage in the preparation 
and sterile filtration of water, particularly drinking water. In addition, 
it can be used for filtering off particulate impurities of all kinds from 
liquids, particularly rinsing liquids, for example in the electronics 
industry, in the manufacture of miniaturized transistor parts, photo 
varnishes and the like. It is also possible to apply the invention to 
clinical purposes, particularly in the case of injection syringes. 
Furthermore, the syringe according to the invention can be used as a 
normally acting or regular syringe, i.e., by withdrawing the piston, a 
liquid medium can be drawn into the interior of the cylinder after which, 
by moving the piston rod together with the piston and the valve 
arrangement disposed therein back into the cylinder, it is possible to 
expel from the cylinder the liquid which is to be filtered. This use is 
then the same as with conventional syringe devices.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The illustrated syringe comprises a first cylinder or barrel 1 in which 
there is displaceably arranged a first piston 2 having a concentric 
extension 7' of reduced diameter at one end thereof serving as a piston 
rod. A piston rod 3 serves to move the first piston 2. In the interior of 
the first piston 2 there is arranged a second piston 4 which can be 
displaced by means of the piston rod 3. The pistons 2 and 4 are provided 
with respective valves 5 and 6 at their ends which are nearer the outlet 
from the syringe. 
The second piston 4 is disposed for displacement within the first piston 2 
in a longitudinal bore 7 forming a second cylinder in the first piston 2. 
On the side of the second piston 4 at which the valve 5 is disposed there 
is a pressure chamber 8 which lies between the two valves 5 and 6. 
Sealing rings 9 are provided to seal off the piston 2 with respect to the 
wall of the first cylinder 1. Sealing rings 10 are provided to seal off 
the second piston 4 with respect to the wall of the longitudinal bore 7. 
For actuation of the piston rod 3, the rod is provided with a handle 11. At 
its closed end, i.e., the end remote from its outlet, the first cylinder 
is provided with a cylinder cover 12 in which there is an aperture 17 
through which the reduced diameter extension 7' of first piston 2 is 
guided. The longitudinal bore 7 within the first piston 2 is closed at its 
end remote from the second cylinder outlet by means of a piston cover 13. 
The first piston 2 is further provided with a stop 14 formed as a 
shoulder. Within a cylinder chamber 16 defined by the part of the cylinder 
1 between the first piston 2 and the cylinder outlet, which is provided 
with a cylinder attachment 15, is a liquid or other medium which is, for 
example, to be filtered, or which is to be removed from the cylinder by 
the action of the pressure of a pressure device within the cylinder 1. It 
is possible to mount on the cylinder attachment 15 a filtering arrangement 
(not shown) which may take the form of a filter holder. 
The valve 6 comprises a valve closure element 18 and a spring 19; and is 
disposed in a bore 26 within the first piston 2. The valve 5 comprises 
likewise a valve closure element 21 and a spring 20, and is disposed in a 
bore 27 within the piston 4. The springs 19 and 20 press the closure 
elements 18 and 21 respectively into valve-closing positions. 
A pressure medium for the pressure chamber 8 is air which can pass through 
an inlet duct 22 having a radial portion 22' through the open valve 5 into 
the pressure chamber 8. 
The illustrated syringe operates in the following manner: 
Starting from a normal position of the device as depicted in FIG. 2A, the 
piston rod 3 is drawn outwardly of the cylinder 1 in the direction of the 
arrow A which displaces the piston 2 within the cylinder 1, when the 
valves 5 and 6 are closed, in the direction of the arrow A. This 
displacement takes place until such time as the stop 14 on the first 
piston abuts the cylinder cover 12. When this happens, for example, a 
liquid which is to be filtered is drawn into the cylinder chamber 16 
through the aperture in the cylinder attachment 15 (FIG. 2B). The piston 2 
is displaced thereby through the aperture 17 in the cylinder cover 12. 
As the liquid is drawn into the cylinder chamber 16, a pumping action 
generated by means of the second piston 4 displaceable in the longitudinal 
bore 7, is used. This pumping action occurs during the reciprocating 
movement of the piston rod 3 and that of the second piston 4. 
As the piston rod 3 is moved in the direction of the arrow A, a negative 
pressure is created within the pressure chamber 8, whereby by reason of 
the force of the spring 19, the valve 6 remains closed so that no liquid 
can pass out of the cylinder chamber 16 into the pressure chamber 8. By 
reasons of the pressure difference obtaining on both sides of the closure 
element 21 of the valve 5, mainly by reason of the pressure difference 
between atmospheric pressure and the negative pressure in the pressure 
chamber 8, the closure element 21 is displaced against the force of the 
spring 20 so that the valve 5 is opened. The outside air can then flow 
through the gap at rod aperture 25 through bore 7, radial aperture 22', 
duct 22 and through valve 5, and then into the pressure chamber 8 until 
more or less atmospheric pressure obtains in the pressure chamber 8. 
The piston rod 3 is then moved in the direction of the arrow B. This 
movement produces in the pressure chamber 8 an over-pressure so that the 
closure element 18 is displaced against the force of the spring 19 into 
its open position, so that the valve 6 in the piston 2 is opened. The 
pressure chamber 8 is then in communication with the cylinder chamber 16 
upstream of the piston 2 in which is the liquid which is to be ejected. 
Upon further movement of the piston rod 3, then, the liquid disposed in 
the cylinder chamber 16 is forced through the aperture in the cylinder 
attachment 15 against the pressure resistance or back pressure built up, 
for example, by a filter arrangement (FIG. 2C). As a result of the 
over-pressure in the pressure chamber 8, which acts on the liquid to be 
expelled, this pressure resistance is overcome. By means of the device 
illustrated, it is readily possible to achieve an over-pressure of 15 atm 
above atmosphere. After the piston 4 has been pressed all the way into the 
longitudinal bore 7, the piston 4 is, by actuation of the piston rod 3, 
withdrawn again in the direction of the arrow A, so that the 
aforedescribed cycle is repeated. By virtue of this pump movement being 
repeated several times, it is possible for the cylinder chamber 16 to be 
completely emptied. It is also possible during the pumping movement to 
achieve accurate dispensing. The forces of the springs 19 and 20 in the 
two valve chambers of the valves 5 and 6 can be regulated by adjusting 
screws 24 and 23. The spring forces are selected as a function of the 
desired pressure which it is intended to apply upon expulsion of the 
liquid from the cylinder chamber 16. Accordingly, so it is naturally also 
possible to adjust the over-pressures to a value less than 15 atm above 
atmospheric, whereby the same amount of force is always required when 
expelling the liquid which is to be filtered. 
The cylinder 1 and the piston 2 can be made from synthetic plastics 
material. If it is required by the nature of the application to which the 
syringe is to be put, they can be of a physiologically sterile material. 
The arrangement illustrated can also be used as a quite conventional 
syringe in that the liquid disposed in the cylinder chamber 16 can be 
forced out by inward movement of the piston 2. 
Obviously, many modifications and variations of the present invention may 
be made with regard to the foregoing detailed description without 
departing from the spirit of the invention.