JPH0331912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a metering pump for fluids having an inlet valve and an outlet valve, the outlet opening from the pump chamber within the action range of the inlet valve. The movable valve member of the inlet valve is of the type formed by a piston having a reciprocating drive and sliding in a cylinder.

BACKGROUND OF THE INVENTION A metering pump of the above type is known from DE 33 31 558 A1. This pump is
Required for accurately and reproducibly metering small quantities of liquid or gaseous media. This pump has a piston guided in a cylinder which periodically carries out suction and discharge strokes by means of a reciprocating drive, for example a crank drive. An inlet valve and an outlet valve are connected to the pump chamber.

A disadvantage of this known metering pump is that during the suction process in the open state of the inlet valve, a pressure drop occurs due to the resistance of the inlet valve, which is generally narrow, and this pressure drop causes a high vapor pressure. In the past, vapor bubbles formed during the transport of liquids, or insufficient filling of the pump chamber occurred when transporting gaseous media. This prevents accurate metering. During the subsequent discharge stroke, during which the liquid is forced out of the pump chamber via the outlet valve, the discharge of the vapor bubbles formed is not guaranteed. For accurate and reproducible metering of extremely small amounts of liquid or gaseous media in the microliter range, the flexibility of each valve is minimal, so that the dispensed metered quantity is completely routed through the discharge conduit. It is necessary that the material can be transported within the container. Furthermore, high conditions must be set for the inlet and outlet valves to avoid leakage. In this known piston metering pump, the inlet valve is opened by the overpressure that develops in the supply conduit;
It cannot be prevented that the medium to be metered flows out via the pump chamber and the outlet valve directly into the supply line. In this case, metering is no longer possible and the medium flows in an uncontrolled manner towards the actuator.

OBJECT OF THE INVENTION It is therefore an object of the invention to improve a piston metering pump of the type mentioned at the outset in such a way that, even during rapid filling of the pump chamber, the formation of vapor bubbles or the formation of negative pressure during the suction phase is avoided. In this case, the waste clearance volume of the piston metering pump is kept small, so that the metered amount can be expelled from the outlet valve with the lowest possible losses. It is.

Means for Solving the Problem The structural means of the invention which solves the above problem consists in that the cylinder is movable by its own cylinder drive which is decoupled from the piston drive.

Operation The main advantage of the invention is that the pumping medium can flow into the pump chamber through the wide cross section of the inlet valve without dynamic pressure losses during the suction stroke. This largely avoids the formation of vapor bubbles even when inhaling liquids with high vapor pressure, such as liquid phase anesthetics. The suction of the gaseous medium takes place without significant pressure losses. In the closed state, there is virtually no pipe line between the inlet valve and the pump chamber that communicates the two, so the ineffective volume during the discharge period is small. In contrast, in the open state, the inlet valve forms an inlet zone of large cross-sectional area surrounding the outer circumference of the pump chamber, so that the piston can carry out a powerful suction stroke in order to fill the pump chamber. The inlet valve is closed before the start of the discharge stroke. The cylinder is driven by a unique drive such that during the suction stroke, the inlet communicates with the pump chamber, and just before the start of the discharge stroke, it moves towards a seal surrounding the outlet, allowing the pump chamber to be emptied via the outlet. The piston is moved synchronously with the reciprocating drive of the piston. Alternatively, it may be considered as an equivalent configuration that the cylinder is fixedly housed in the pump casing, the valve casing is configured as a movable part of the inlet valve, and the valve casing is controlled by a drive device. However, such an arrangement requires high costs for sealing the relatively movable parts.

Embodiment In a preferred embodiment, the movable member of the inlet valve is constituted by the ring seal itself, which surrounds the outlet and is inflatable towards the valve face by means of a control pressure. In that case, the ring seal is adapted to be expanded into the valve chamber by the control pressure until it abuts its seat surface. This controllable ring seal can be arranged on the piston side or on the outlet side depending on the purpose. A ring seal of simple construction consists of a ring diaphragm housed in an annular groove, with the control pressure conduit being connected to the annular groove. The timing of the control pressure generation is synchronized to the piston movement, as described for the moving cylinder. The pressure generating medium may be in a liquid phase or a gas phase. If the cylinder is movable, the remaining stroke from the closing of the ring seal to the resting of the cylinder on the fixed stop is involved in metering as an extra stroke. The equivalent is
This also applies if the cylinder is stationary and the ring diaphragm can be expanded by controlled pressure.
Therefore, in order to eliminate such extra strokes, a movable cylinder and a controllable ring seat are combined, and the ring seal is activated only when the cylinder comes into contact with a fixed stopper and stops. .

According to an advantageous embodiment of the invention, the cylinder is guided coaxially with respect to the piston and a flexible length compensation element is arranged on the cylinder drive. In order to firmly and precisely close the pump chamber by means of the inlet valve, the cylinder is moved towards the ring seal until it rests against the surface surrounding it, thereby closing the pump chamber at the end of the delivery stroke. In this case, a piston seal with a beveled end face runs into the correspondingly capped entry surface of the outlet, so that the pump chamber can be completely emptied. If air bubbles are present, they are simultaneously pushed out of the pump chamber.
In addition, even if the length errors between the cylinder and the drive mechanism for cylinder stroke movement are different, a flexible length compensation mechanism compensates for each error in order to ensure a tight contact. Do this.

According to the invention, it is further advantageous if the outlet valve consists of a ball valve, which is followed by a prestressed dish valve. This ball valve closes off the waste clearance volume created by the outlet to the dish valve and allows an accurate and reproducible conveyance of the metered amount present in the pump chamber, making it possible to reduce the variability of said pump chamber. be extremely small. The valve chamber of the ball valve is closed in the transport direction by a prestressed dish valve. The flexibility of the flat seal of the dished valve does not create unnecessary clearance due to the intervening ball valve. When the dish valve is not completely sealed, the ball valve prevents liquid present in the conveying conduit behind the dish valve from flowing back when the inlet valve is opened. Conversely, in a sealed dish valve and an unsealed ball valve, only the amount existing between the two will be flushed back. The valve body opens only when the metered quantity delivered by the delivery stroke of the piston exceeds its closing pressure.
If an unfavorable pressure is inadvertently built up in the supply conduit up to the inlet valve (which can occur, for example, if the stock container is insufficiently evacuated and heated), the closing force of the dish valve is is selected to prevent uncontrolled flow of medium through the metering pump in the open state of the inlet valve.
Owing to the mutually adapted shapes of the beveled piston end face and the capped inlet face, steam bubbles can be forced out if they reach the pump chamber. This is the case, for example, when a stock container for a liquid medium becomes empty and air is sucked in.

Polytetrafluoroethylene is particularly preferably used as material for the manufacture of the cylinder, since this material has good frictional properties between the cylinder head seal and the running surface in the cylinder and the required outer seal. , which is better than that of similar, also suitable materials such as hard metals, sapphire, aluminum oxide ceramics or amorphous glass graphite.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The piston metering pump shown in FIG. 1 consists of a pump casing 1, a valve casing 2 and a movable cylinder 10 accommodated in the pump casing. The valve casing 2 houses a dish-shaped valve consisting of a valve body 3 and a seal crater 20, and a ball valve consisting of a ball 6 and a valve seat 7. Movable cylinder 10
A piston 11 is slidably disposed inside. The inlet 23 is connected to an inlet chamber 29 . Valve housing 2 has a cap-shaped inlet face 30 for outlet 8 towards pump chamber 9 . This outlet 8 is closed by a ball 6 which is pressed onto the valve seat 7 via a conical coil spring 25. The valve chamber 5 of the ball valves 6 and 7 has a seal crater 2
It is covered by a flat seal 4 located within the dish-shaped valve along 0. The dish valves 3, 20 are held together by pressure springs 22 and have a plurality of guide ribs 24 between which an outflow passage is formed.

The piston drive 16 is designed as a clamper device and serves to generate a reciprocating suction and discharge stroke of the piston 11 along the inner surface of the cylinder 10. The piston 11 is sealed to the cylinder 10 by a piston seal 14 located at its head end. This piston seal 14 is made of polytetrafluoroethylene (PTFE), for example, when a liquid anesthetic agent is pumped. The cup-shaped piston seal 14 is hooked into the groove of the piston 11 by a rib on its inner surface. A piston ring-shaped sealing lip is arranged on the outer surface of the piston seal 14, and this sealing lip is brought into contact with the cylinder 10 by a spring member arranged between the piston 11 and the piston seal 14. The end face 32 of the piston seal 14 has a convex shape adapted to the above-mentioned cap-like inlet face 30. Guidance of the piston is provided by a piston bearing 15.

The cylinder 10 is guided in the pump housing 1 so as to be movable coaxially with respect to the piston 11 by means of its own cylinder drive 17 and a rod 19 as a rocking member, so that the cylinder 10 A movable valve member for the inlet valve consisting of a ring seal 13 is formed. The seal of the cylinder 10 to the pump casing 1 is
This is accomplished by a lip seal 12 made of polytetrafluoroethylene (PTFE), and the cross section of this lip seal 12 is U-shaped. A spring element is inserted into the U-shaped cutout of the lip seal 10 and presses both lip parts against the surface to be sealed.

Next, the operating type of the metering pump according to the present invention will be explained.

At the time of operation according to FIG. 1, the medium in the pump chamber 9 has been completely pushed out through the outlet 8 by the forward-swiped piston 11, after which the cylinder 10 is moved against the ring seal 13 by means of the cylinder drive. The inlet valve 10 is spaced apart from the abutment part, and
13 will be released. Then the piston drive device 16
is rotated half a revolution in one go, so that the medium to be metered, for example a liquid anesthetic agent, is sucked into the expanding pump chamber 9 via the inlet 23 . At the end of the suction stroke, the cylinder 10, whose end face is the valve casing 2,
It is caused to run toward the ring seal 13 until it comes into contact with the surface facing the cylinder 10. This closes the inlet valves 10, 13 and allows the compression stroke of the piston 11 to begin. Depending on the particular requirements and the control of the piston drive 16, the contents of the pump chamber 9 can be transferred to the outlet 8, the ball valves 6, 7 and the dish valve 3 in one complete delivery stroke or in a series of partial stages. , 20 through the outflow opening 21 to the actuator. When the piston reaches the top dead center, the end surface of the piston seal 14 comes into contact with the inflow surface 30. This completes one full pumping cycle.

FIG. 2 shows a partial cross-sectional view of one embodiment of the length compensation mechanism 19 along line 2--2 in FIG. In this case a cylinder 10 with a cylindrical bore 26
Only one slit 26 is shown, and this hole 26 has two slits 28 at right angles to its longitudinal axis. Inside each slit 28 are two rods 1.
The spherical end 31 of the rocker member 9 is slidably guided. The two rods 19 are interconnected via a web 27 at the pivot point of the length compensation mechanism. At the end of one cylinder stroke, the cylinder 10 is in tight contact with the end face of the valve housing 2. Next, cylinder drive device 1
The remaining stroke of 7 is taken up by the elastic deflection of the rocker member 19.

[Brief explanation of drawings]

The drawings show one embodiment of the invention,
FIG. 1 is a sectional view of the piston metering pump, and FIG. 2 is a partial sectional view taken along line 2--2 in FIG. 1, showing the length compensation mechanism. 1... Pump casing, 2... Valve casing, 3... Valve body, 4... Flat seal, 5... Valve chamber, 6... Ball, 7... Valve seat, 8... Outlet, 9...
Pump chamber, 10... Cylinder, 11... Piston, 12... Lip seal, 13... Ring seal, 14... Piston seal, 15... Piston support, 16... Piston drive device, 17... Cylinder drive device , 19... Rod, 20... Seal crater, 21... Outflow opening, 22... Pressing spring, 23... Inlet, 24... Guide rib, 25...
...Conical coil spring, 26...Cylindrical hole, 27...
Web, 28...slit, 29...entrance chamber, 3
0... Inflow surface, 31... End, 32... End face.

Claims (1)

[Scope of Claims] 1. A metering pump for fluid comprising an inlet valve and an outlet valve, wherein the outlet from the pump chamber opens within the action range of the inlet valve, and the movable valve member of the inlet valve , which has a reciprocating drive and is formed by a piston sliding inside the cylinder, in which the cylinder 10 is connected to a piston drive 16.
Unique cylinder drive device 1 disconnected from
A piston-type metering pump, characterized in that it is movable by 7. 2. The movable valve member of the inlet valve 10, 13 is constructed as a ring seal 13 surrounding the outlet 8 and capable of being inflated towards the valve face by means of a control pressure. Metering pump as described. 3. Metering pump according to claim 2, wherein the cylinder 10 is coaxially guided with respect to the piston 11 and the cylinder drive 17 has a flexible length compensation mechanism 19. . 4 The outlet valve is a ball valve 6, 7 and a preloaded dish valve 3, 20 downstream of the ball valve.
A metering pump according to claim 1, comprising: 5. The piston end surface 32 is formed in a convex shape, and the outlet 8 is surrounded by an inflow surface 30 formed in a concave shape corresponding to the convex surface.
A metering pump according to claim 1. 6. The metering pump according to any one of claims 2 to 4, wherein the cylinder 10 is made of zirconium oxide ceramic.