Gas separation: apparatus – Apparatus for selective diffusion of gases – Membrane to degasify liquid
Patent
1997-05-09
1999-02-16
Spitzer, Robert
Gas separation: apparatus
Apparatus for selective diffusion of gases
Membrane to degasify liquid
95 46, B01D 1900
Patent
active
058715665
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
1. Field of the Invention
This invention relates generally to a metering pump for the measured delivery of liquids from a supply into a metering pipe, and more particularly to a metering pump that is vented to permit pressurized liquid being pumped to be removed in a degassing space where the pressure is below the liquid pressure and discharged.
2. Discussion of Related Art
In the pumping and metering of liquids, the reproducibility of delivery and the intake behavior can be seriously affected by outgassing of the liquid. Gas present in the liquid to be delivered is compressed during the compression stroke and can expand again during the following suction stroke. Accordingly, only part--if any--of the liquid is actually pumped. If the metering pump operates with a low stroke volume, even small amounts of gas can lead to serious metering errors. In addition, gas can be compressed in the pump chamber during pumping and can expand during the intake of liquid so that the intake and hence the delivery of the liquid by the metering pump is impaired. Accordingly, it is standard practice to fit metering pumps with a venting system.
A metering pump with the features mentioned at the beginning is known from DE 42 41 030 C1. The venting system comprises a vent valve located between a pressure valve of the pump chamber of the metering pump and the output side of the pump where there is a pressure valve leading to a metering pipe. The vent valve opens during the suction stroke and closes during the compression stroke. During the suction stroke when the pressure valve is closed, gas is able to escape through the opened vent valve. Although this metering pump has proved successful in practice, its use for aggressive or sensitive liquids can lead to difficulties, particularly with regard to the moving valve parts.
SUMMARY OF THE INVENTION
By contrast, the problem addressed by the present invention is to improve a metering pump with the features mentioned above in such a way that its venting system performs the necessary degassing function without the use of parts, for example moving valve parts, whose function is dependent on the more or less aggressive properties of the liquid to be transported.
According to the invention, the solution to this problem is provided in one embodiment by a venting system comprising a semipermeable membrane which, on one side, is exposed to the pressurized liquid and which, on its other side, immediately adjoins the degassing space.
It is important to the invention that the semipermeable membrane used is one which continuously and effectively separates the liquid to be transported from the degassing space. Accordingly, this semipermeable membrane is capable of further transporting the liquid in the manner of a pipe wall because it represents an impenetrable obstacle to the liquid. However, the gas transported by the liquid is able to diffuse through the membrane so that the gas phase is separated. The semipermeable membrane can be made resistant to pressure and chemicals so that aggressive properties of the pressurized liquid to be transported have no effect on the function of the membrane. So far as the liquid is concerned, the venting system equipped with this membrane forms a completely closed-off area between the metering pump and the metering pipe. There is no need for any mechanisms operating in dependence upon the pump frequency. On the contrary, the membrane acts permanently, even during the compression stroke of the metering pump, which is of advantage in terms of effective degassing of the liquid to be transported. In addition, the membrane provides for considerable structural simplification of the region between the metering pump and the metering pipe, all by reducing the number of necessary parts and using parts which present no sealing or durability problems as is the case with the known venting systems with valve constructions. The semipermeable membrane can readily be made and fitted with such a level of pressure resistance that interference with the delivery vol
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Jaeschke Wayne C.
Lang Apparatebau GmbH
Spitzer Robert
Szoke Ernest G.
Watov Kenneth
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