WO1989003483A1

WO1989003483A1 - Float accumulator

Info

Publication number: WO1989003483A1
Application number: PCT/NO1988/000078
Authority: WO
Inventors: Per B. Andersen
Original assignee: Andersen Per B
Priority date: 1987-10-14
Filing date: 1988-10-13
Publication date: 1989-04-20
Also published as: SE9001325D0; SE464658B; SE9001325L; NO163031C; NO874286D0; NO163031B; NO874286L

Abstract

The present invention relates to a hydro-pneumatic accumulator of the float type, preferably for use to store energy in connection with a hydraulic system which is to receive and deliver, respectively, large quantities of working fluid during a short period of time. The accumulator consists of a vertical container (1, 2, 4), and a free swimming float (5) which serves to separate the accumulator's content and gas and fluid, and to work together with a seal ring (6) in the end cover (4) as a valve which prevents the gas from escaping from the accumulator if it is completely emptied for fluid.

Description

FLOAT ACCUMULATOR

The present invention relates to a hydro-pneumatic accumulator, preferably for use in connection with a hydraulic system which is to receive and deliver, respectively, large quantities of working fluid during a short period of time. Other relevant use will be absorbing of surge waves, - acting as an emergency source of power to maintain the pressure in a system or manipulate valves in cases when the normal power supply fails, - operating in cooperation with hydraulic cylinders as a spring or a counter balance weight a.o.

A hydro-pneumatic accumulator consists principally of a container which is filled with compressed gas and connected to a system containing a liquid. When charging the accumulator, liquid is pumped into it and the gas is further compressed until a set maximum pressure is reached. When the accumulator shall supply energy in form of working liquid, the system pressure is reduced and the gas expand and press liquid back into the system.

In the accumulator, the gas is usually separated from the liquid by means of a piston, a bladder, a diagraph, or a float. The different types of accumulators are often named in accordance with how this separation takes place. For instance piston accumulator, bladder accumulator, float accumulator etc

Further the accumulators usually contain an arrangement which prevent the gas from escaping into the system in cases when the system pressure is lower than the precharge pressure of the gas. I.e. in cases when the accumulator is completely empty for liquid. In piston accumulators, this is taken care of by seal rings between the piston and the cylinder wall. In bladder accumulators there are usually a spring loaded valve in the liquid outlet which is being closed by the bladder when the accumulator is emptied for liquid. In a float accumulator the float usually act as a valve which close the liquid outlet when the accumulator is empty for liquid. The piston accumulator and the bladder accumulator are the most common types, and description can be found in most technical literature about hydraulic equipment.

The present invention relates, however, to the category "float accumulators" , and will in the following be described referring to the drawing fig.1 which illustrates a section through an appropriate embodiment of an accumulator.

The accumulator consists of a cylindrical shell (1) which is closed in the upper end by a cover (2) which contain a gas filling valve (3). In the lower end the shell is closed by a cover (4) which contain a boring (a) which is connected to a hydraulic system. Item 1,2,4 create accordingly a container which contain a free swimming float (5) which separate the gas from the liquid. The gas and the liquid will be in contact with each other in a narrow ring area (b) around the float (5) only. On the upper side of the float the accumulator has a body of compressed gas which pressure will depend on the level of the liquid, and accordingly on the position of the float. When liquid is pumped into the accumulator through boring (a), the compressed gas will be further compressed. When the hydraulic system which is connected to the accumulator via the boring (a) require a large quantity of liquid, the pressure in the system will drop and the gas over the float (5) will expand and press liquid out through the boring (a).

In the lower end cover (4), a seal ring (6) is installed which together with the float (5) work as a valve closing the boring (a) when the float (5) is in it's lowermost position. Thus the seal ring .6. is included in an end valve system which does not require movable parts. The seal ring (6) prevent leakage of gas out into the hydraulic system when the system pressure is lower than the precharge pressure of the gas and the float (5) therefore is in the bottom position. I.e. when the accumulator is emptied for liquid. If a float accumulator shall work properly under different working conditions, the following requirements should be fulfilled:

1. The float must close the outlet to the hydraulic system when the system pressure is lower than the gas precharge pressure.

2. The float must withstand a high working pressure (50-300 bar) and at the same time have a low specific weight so it floats in the actual liquid.

3. The float must prevent the gas from being absorbed by the liquid and thereby escaping from the accumulator mixed with the liquid.

Requirement No. 1 is fulfilled for the present invention due to the previously described seal ring (6).

When designing, the following precautions have been taken to fulfill requirement Nos. 2 & 3;

The float (5) has a relatively long axial elongation and has a circumferential guide (7) at the lower part of the float which has a very small clearance (c) to the shell (1). Further the float (5) is equipped with a guide (8) at the upper part of the float with a clearance (d) to the shell (1). Between the two guides (7,8), there is a ring chamber (e) limited by the shell (1) and the float (5). The gas and the liquid meet in a ring area (b) and the liquid in the ring chamber (e) will be saturate by gas. Due to the small gap (c) at the guide (7) however, the liquid level in the chamber (e) will be almost constant,- even at accelerated and decelerated movement of the float. The gas saturate liquid in chamber (e) will therefore to a very little extent be changed out with the liquid below the float (5). Accordingly the gas is prevented from mixing with the system liquid. The float's (5) long axial dimension gives an excellent guide which ensures that the float can move axially almost without friction. This is important for keeping the liquid level in chamber (e) constant. Further the long axial elongation ensures that liquid does not advance over the top of the float (5) or gas under the bottom of the float (5) even at a very fast accelerated or decelerated movement of the float (5). Due to the same reason, the float's (5) specific weight should make the float (5) submerged approx. 1/2 of it's height in the actual liquid.

To obtain a float with so low specific weight that it will be half submerged in a liquid (for instance oil) and at the same time be strong enough to withstand a high external pressure, the float (5) is produced with a core of syntactic foam (10) surrounded by a gas tight cover (9). Syntactic foam, consisting of micro spheres in a matrix, is well-known as buoyancy bodies in connection with sub-marines and sub-sea installations, but alone it is not very usable when it is exposed by compressed gas. The gas pressure will, during a period of time, diffuse into the micro spheres and blow them to pieces when the pressure is released.

The core (10) is therefore completely surrounded by a gas tight shell (9) which has good mechanical qualities in a wide temperature range and has chemical resistance against the actual liquid. (For instance POM). As micro spheres in the syntactic foam of the core (10) a material which improve the heat extension and the elasticity of the matrix should be used. (For instance glass). This is important for the possibility to make the gap (c) between the guide (7) and the shell (1) small and keep it small under different temperature and pressure conditions. This is necessary to ensure that the separation of gas and liquid is sufficient. The present invention can be compared with previous patent claims for accumulators and similar devices which contain free swimming floats, for instance DE3143890A1, US 1.959.640, and US 2.317.796. These are devices which are intended for a low working pressure, and produced by materials which were known at the time when the inventions were made, the floats would not withstand the working pressure which is actual for the accumulator covered by the present claim. Alternatively the floats would be too heavy to swim half submerged in a liquid like oil. In addition some of the previous claims describe a float design which gives a poor separation of gas and liquid. Further, some have an insufficient end valve system for preventing gas from escaping from the accumulator to the hydraulic system when the accumulator is empty for liquid.

Claims

PATENT CLAIM

Hydropneumat ic float accumulator comprising a housing (1,2,4), and a float (5) arranged therein to separate the accumulator's content of liquid from the content of gas and to work together with a seal ring (6) in the end cover (4) as a valve which prevent the gas from escaping from the accumulator if it is completely emptied for liquid, characterized in that the float (5) is formed as a cylindrical container consisting of a core (10) made of syntactic foam covered by a gas proof shell (9).