EP1600696A1

EP1600696A1 - Venting of a closed hydraulic pressure system

Info

Publication number: EP1600696A1
Application number: EP05076110A
Authority: EP
Inventors: Frank Gerard Rieck; Jan Henk Cnossen
Original assignee: Flamco BV
Current assignee: Flamco BV
Priority date: 2004-05-18
Filing date: 2005-05-11
Publication date: 2005-11-30
Also published as: NL1026222C1

Abstract

In a closed hydraulic pressure system with a system wall, the system wall (3) is provided, in a region (4) of the system where free gases present in the system can be discharged, with a porous element (1) which allows free gases present in the system to pass through it but is sealed with respect to the liquid that is present in the system. This element is compact and can be designed so as to be exchangeable.

Description

The invention relates to a closed hydraulic pressure system as is known from heating or cooling systems. It is known that in a system of this type a certain amount of gases can be bound in the liquid, depending on pressure and temperature. Since the physical conditions for the liquid in the system are often not constant, gases may be released in the system. This effect may be boosted further if liquid is added to a closed hydraulic system, with the liquid added previously having been stored or supplied under conditions which differ from those prevailing in the system. These phenomena are known and are described in Henry's law.

These free gases need to be discharged from the hydraulic system, since they may have an adverse effect on correct operation of the system. It is known to discharge the free gases that are present in the system with the aid of a float bleed vent. A float bleed vent of this type is generally positioned at the highest point or another gas collection point of the hydraulic system and comprises a valve which is actuated by a float floating on the liquid. When gas is formed, this gas will collect at the highest point or gas collection point. The increase in the quantity of gas collected will cause this gas to displace the liquid at the location of the float. As the liquid level drops, the float also drops, until the valve connected to the float is opened. As a result, the free gases are discharged and the liquid level rises again until the float closes the valve.

One drawback of the float bleed vent is that a relatively large amount of space is required for the necessary components, and that a small quantity of gas will always remain behind in the system. The valve closure is often also critical and is susceptible to soiling, resulting in a deterioration in the closure.

It is an object of the invention to provide a closed hydraulic pressure system with a gas discharge member which does not have the above drawbacks.

According to the invention, this object is achieved by a closed hydraulic pressure system according to claim 1.

A porous element used as gas discharge element in accordance with the invention can be of extremely compact design, unlike a float bleed vent. Moreover, a gas discharge element designed as a porous element is reliable since it comprises no moving parts. The element may be designed to be exchangeable.

Preferred embodiments of the system according to the invention are defined in the dependent claims.

The desired degree of porosity of the porous element depends on the viscosity and density of the liquid, the nature of the free gases and the pressure and temperature in the hydraulic system. The element will have to be able to allow the gases to pass through but remain impervious to the liquid.

The size of micro-openings (pores) in the porous element should be such that the property of allowing free gases to pass through on one side, while at the same time blocking the liquid, is maintained at the temperature and pressure prevailing in the hydraulic system with respect to the atmosphere or environment.

Depending on the desired effect, it is conceivable to use embodiments in which all the free gases are discharged from the system ranging through to an embodiment in which a minimal quantity of free gases are retained in a closed hydraulic system. The latter option may be valuable if an integrated expansion space is desirable in order to be able to absorb changes in volume of the liquid resulting from changes in temperature of the liquid.

The invention will be explained in the following description of a number of embodiments with reference to the drawing, in which:

Fig. 1 shows a section of a closed hydraulic pressure system provided with a porous element in accordance with the invention,

Fig. 2a and 2b show an expansion tank which is connected to a hydraulic system according to the invention, is provided with a separation membrane and has a porous element arranged in the wall, in two states,

Figs. 3a-3c show a membrane-free expansion tank, which is connected to a hydraulic system according to the invention and has a porous element arranged in the wall, in three states,

Fig. 4 shows a gas discharge member with a tubular porous element which is to be connected to a hydraulic system according to the invention, and

Fig. 5 shows a gas discharge member with a tubular porous element which is fitted in a pipe part of a hydraulic system according to the invention.

Figure 1 shows an embodiment of a section 2 of a closed hydraulic pressure system according to the invention provided with a porous element 1. The porous element 1 is in the form of a panel which is arranged in the wall 3 of a gas collection part 4 which is arranged on a pipe part 5 of the hydraulic system and the interior of which is in communication with the interior of the pipe part 5. A gas collection part 4 of this type will be arranged at a location where free gases will collect, such as the highest point or another gas collection point in the system. The free gases will be discharged via the porous element, which is impervious to the liquid.

Figures 2a and 2b illustrate an expansion tank 11 connected to a hydraulic system according to the invention, a separating membrane 13 being arranged substantially vertically between the gas section 12 in the expansion tank 11 and the liquid section 12. The liquid section 12 of the expansion tank 11 is connected at the bottom, by means of a connection line 14, to the remainder of the hydraulic system (not shown). It is known that with this type of expansion tank, gas (air) which remains behind in the liquid section 12 is difficult to discharge. A float bleed vent is difficult to position, in particular in relatively small expansion tanks. In the expansion tank 11 illustrated in Figs. 2a-2b, a porous element 16 in the form of a panel is arranged in the wall 15 of the liquid section 12, specifically in the vicinity of the highest point. Free gases 17 that are present in the liquid section 12 (cf. Fig. 2a) can be effectively discharged via this porous element 16 (cf. Fig. 2b).

Figs. 3a-3c illustrate a membrane-free expansion tank 12 which is connected to a hydraulic system according to the invention, a porous element 23 in the form of a panel being arranged in the wall 22 of the expansion tank. At the bottom, the expansion tank 21 is connected via a connecting line 24 to the remainder of the hydraulic system, of which a pipe part 25 is illustrated in Figs. 3a-3c.

In a certain position of the expansion tank 21 in a hydraulic system, the quantity of free gas 26 present in the expansion tank 21 may become too great. This will lead to the liquid level 27 in the expansion tank 21 becoming too low. To reduce this quantity of free gas 26, the excess gas is discharged via the porous element 23 arranged in the wall 22 (cf. Fig. 3c). As soon as the excess gas has been discharged via the porous element 23, the liquid level 27 rises, with the result that the porous element 23 is completely covered with liquid. Since the porous element 23 only allows gases to pass through but remains impervious to liquid, the expansion tank 21, and therefore the hydraulic system, are once again completely closed.

Fig. 3 also shows where the liquid level 25 is located during normal operation of the expansion tank 21. In Fig. 3b, the quantity of gas 26 has reached a level which is too low. A float 28 moves upwards with the liquid level 27, with the result that a valve 29 coupled to the float 29 is opened, and the gas space 26 is connected to a gas reservoir 30 which is separately connected to the expansion tank 21 and contains gas at a higher pressure. The expansion tank 21 is filled with gas from this reservoir 30 until a new equilibrium is found. The liquid level 27 and therefore the float 28 drop, with the result that the valve 29 coupled to the float 28 - and therefore the supply of gas from the reservoir 30 - is closed again.

Fig. 4 shows a gas discharge member 41 with a tubular porous element 42 which is to be connected to a hydraulic system according to the invention. The gas discharge member 41 comprises a substantially cylindrical housing 43 which is closed off by a threaded cover 44 at the top side. At the underside, the housing 43 is provided with an externally threaded tubular connection part 45 which can be screwed into an opening provided with a mating internal screw thread (not shown) in a hydraulic system. The tubular porous element 42 is arranged substantially concentrically in the housing 43, and is retained in a sealed manner at the end side between a sealing member 46 arranged in the cover 44 and a sealing member 48 arranged at the location of the base 47 of the housing 43. The interior 49 of the tubular porous element 42 is therefore in communication with the interior of the tubular connection part 45. One or more openings 51 are arranged in the wall 50 of the housing 43, through which gases which have been discharged from the hydraulic system via the porous element 42 can be discharged to the environment.

It will be clear that the gas discharge member 41 is connected to a location on the hydraulic system at which gases will collect, such as the highest point or another gas collection point of the system.

Fig. 5 illustrates a gas discharge member 51 with a tubular porous element 52 which is mounted in a pipe part 53 of a hydraulic system according to the invention. The design of the gas discharge member 51 fundamentally corresponds to the gas discharge member 41 shown in Fig. 4.

The gas discharge member 51 likewise comprises a substantially cylindrical housing 54 which on one side is closed off by a threaded cover 55 which is provided with a tubular connection part 56 provided with an internal screw thread. On the other side, the housing 54 is provided with an internally threaded tubular connection part 57. Externally threaded

end parts

58 and 59 of the pipe part 53 of the hydraulic system are screwed into the

tubular connection parts

56 and 57, respectively. In this embodiment too, the tubular porous element 52 is arranged substantially concentrically in the housing 54, and at the end side it is retained in a sealed manner between a sealing member 60 arranged in the cover 55 and a sealing member 62 arranged at the location of the base 61 of the housing 54. The interior 63 of the tubular porous element 52 is therefore in communication with the interior of the pipe part 53.

One or more openings 65 are arranged in the wall 64 of the housing 54, through which gases which have been discharged from the hydraulic system via the porous element 52 can be discharged to the environment.

The gas discharge member 51 will likewise be arranged at a location in the hydraulic system where gases will collect, such as the highest point or another gas collection point of the system.

The tubular

porous element

42 or 52 illustrated in Figs. 4 and 5 has an external diameter of, for example, 14 mm and an internal diameter of, for example, 8 mm.

The porous element may be made from various materials, for example a ceramic material, a sintered material, a plastics material or a natural material and may take various forms. By way of example, it may be designed as an element in panel or tube form. In certain cases, it may be designed as a semi-permeable membrane.

It is preferable for the porous element to have a pore size on the liquid side of between 0.1 and 1 µm, preferably 0.2 µm.

The porous element may comprise a plurality a layers with different pore sizes, in which case, by way of example, the layer located on the outer side (atmosphere) has a pore size of between 1 and 15 µm, preferably between 2.5 and 8 µm, and the layer located on the liquid side has a pore size of between 0.1 and 1 µm, preferably 0.2 µm.

As an additional measure to prevent water from leaking through the porous element, the porous element may be provided with a layer of hydrophobic material on the liquid side.

Claims

Closed hydraulic pressure system having a system wall, in which the system wall is provided, in a region of the system where free gases present in the system can be discharged, with a porous element which allows free gases present in the system to pass through it but is impervious to liquid that is present in the system.
Closed hydraulic pressure system according to claim 1, in which the porous element is made from a ceramic material, a sintered material, a plastics material or a natural material.
Closed hydraulic pressure system according to claim 1 or 2, in which the porous element has a pore size on the liquid side of between 0.1 and 1 µm, preferably 0.2 µm.
Closed hydraulic pressure system according to one of claims 1-3, in which the porous element comprises a plurality of layers with different pore sizes.
Closed hydraulic pressure system according to claim 4, in which the layer located on the outer side (atmosphere) has a pore size of between 1 and 15 µm, preferably between 2.5 and 8 µm, and the layer located on the liquid side has a pore size of between 0.1 and 1 µm, preferably 0.2 µm.
Closed hydraulic pressure system according to one of claims 1-5, in which the porous element is provided with a layer of hydrophobic material on the liquid side.
Closed hydraulic pressure system according to one of claims 1-6, in which the porous element is in panel form.
Closed hydraulic pressure system according to one of claims 1-6, in which the porous element is in tube form.
Closed hydraulic pressure system according to one of claims 1-8, in which the porous element is designed as a semi-permeable membrane.
Closed hydraulic pressure system according to one of claims 1-9, in which the porous element forms part of the system wall.
Closed hydraulic pressure system according to claim 10, in which the porous element is arranged in the wall of a gas collection part arranged in the system.
Closed hydraulic pressure system according to claim 10, in which the porous element is arranged in the wall of the liquid section of an expansion tank arranged in the system.
Closed hydraulic pressure system according to one of claims 1-12, in which the porous element is arranged in a gas discharge member, in particular a bleed vent, mounted on the system or in a pipe part of the system.