WO1988002070A1

WO1988002070A1 - A fluid-displacement machine

Info

Publication number: WO1988002070A1
Application number: PCT/DK1986/000103
Authority: WO
Inventors: Anton SO^/RENSEN
Original assignee: Westergaard, Knud, Erik
Priority date: 1986-09-10
Filing date: 1986-09-10
Publication date: 1988-03-24
Also published as: EP0282478A1

Abstract

In a fluid-displacement machine of the piston/cylinder type and with two seals (18, 21; 19, 22; 20, 23) for each piston (4; 5; 6), the intermediate spaces (24; 25; 26) between the seals are interconnected through a duct (30). With this arrangement, the pressure due to leakage from the high-pressure side in all intermediate spaces will be reduced. In a preferred embodiment, the high-pressure seals (18; 19; 20) are of the one-way type allowing comparatively free flow towards the working chamber (7; 8; 9) of the particular cylinder. With this arrangement, the pressure in the intermediate spaces will be kept at or close to the supply pressure, thus preventing any substantial leakage past the low-pressure seals (21; 22; 23), and at the same time allowing fluid having leaked out past the high-pressure seal in one cylinder to be re-introduced into the system past the one-way high-pressure seal of at least one other cylinder, the latter being in the suction or filling phase of its operating cycle.

Description

A fluid-displacement machine.

TECHNICAL FIELD

The present invention relates to a fluid-displacement machine of the kind set forth in the preamble of claim 1.

In the following specification, the present invention will be described with reference to pumps for liquids, but persons skilled in the art relating to fluid-displacement machines of the piston-and-cylinder type will realize that the invention may also by applied to other piston-and-cylinder machines, such as hydraulic motors.

BACKGROUND ART

If in machines of this kind there is a certain amount of leakage through the high-pressure seal, then the pressure in the intermediate space will rise quickly, thus increasing the pressure on the low-pressure seal and consequently also increasing the risk of leakage through the low-pressure seal, e.g. to the surroundings.

DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide a fluid-displacement machine of the kind referred to initially, in which the risk of leakage through the low-pressure seal is considerably reduced if not eliminated, and this object is attained in a machine exhibiting also the the features set forth in the characterizing clause of claim 1. With, this arrangement, any fluid leaking through the high- -pressure seal in one cylinder will be distributed among the intermediate spaces of all the cylinders in the machines, so that the rise in pressure in the intermediate space will be reduced, with a consequent reduction of the risk of leakage through the low-pressure seal.

With the preferred embodiment set forth in claim 2, the pressure in the interconnected intermediate sealing spaces of all cylinders is kept at a value close to the supply pressure, i.e. comparatively low, so that a further reduction of the risk of leakage through the low-pressure seal is obtained.

With the further preferred embodiment set forth in claim 3, there will be at least one cylinder, the working chamber of which is at a pressure equal or close to the supply pressure, thus ensuring that the function of the feature set forth in claim 2 is continuous.

BRIEF DESCRIPTION OF THE DRAWING

In the following detailed specification the present invention is explained with reference to the drawing, which in a single Figure in a highly diagrammatic manner shows an exemplary embodiment of a three-cylinder pump constructed according to the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The exemplary embodiment of a piston-and-cyllnder machine shown in the Figure constitutes a three-cylinder pump with cylinders 1, 2 and 3 with cooperating plunger pistons 4, 5 and 6 respectively. The cylinders 1, 2 and 3 are shown as constituting parts of a pump body (not shown), that may be common to the three cylinders 1, 2 and 3, the working chambers 7, 8 and 9 of which constitute cylindrical bores in the pump body. The pistons 4, 5 and 6 in the three cylinders 1, 2 and 3, angularly spaced by 120°, are driven in a reciprocatory motion by a common eccentric cam 10 carried on or integral with a drive shaft 11 adapted to be driven by a suitable motor (not shown).

Components not directly relevant to the present invention are not shown in the Figure, such as inlet and outlet valves connected to or placed in inlet ducts 12, 13 and 14 and outlet ducts 15, 16 and 17 communicating with each working chamber 7, 8 and 9 respectively, as well as return springs adapted to keep the pistons 4, 5 and 6 in contact with the rotating eccentric cam 10. Such components will be known to persons skilled in this art.

Further, it should be noted that the invention is not limited to pumps of the known "star configuration" shown, as it may be applied with the same effect to pumps and other piston machines, such as hydraulic motors, of various configurations, such as having a number of axially parallel cylinders, the pistons of which are reciprocated by a common so-called swash plate or the like.

Each of the cylinders 1, 2 and 3 comprises two sealing rings, viz. a primary sealing ring 18, 19 and 20 respectively and a secondary sealing ring 21, 22 and 23 respectively. The primary sealing rings 18, 19 and 20 provide seals between each cylinder's working chamber 7, 8 and 9 respectively and an intermediate sealing chamber 24, 25 and 26 respectively, while the secondary sealing rings 21, 22 and 23 provide seals between the intermediate sealing chambers 24, 25 and 26 respectively of each cylinder 1, 2 and 3.

The pressure difference across each primary sealing ring may be defined as the primary leakage pressure, and that across the secondary sealing rings as the secondary leakage pressure. Obviously, the primary leakage pressure is the difference between the pressure in the working chamber and the pressure in the intermediate sealing chamber, and the secondary leakage pressure is the. difference between the pressure in the intermediate sealing chamber and the external space.

In operation, the pressure in each working chamber 7, 8 or 9 will vary cyclically depending on the direction of movement and the position of the piston, so that during a filling stroke, with the piston moving away from the end of the cylinder containing the inlet and outlet ducts, the pressure will be approximately the same as (or a little lower than) the supply pressure, whereas during a de- very stroke with the piston moving towards said end of the cylinder, the pressure will be approximately the same as (or a little higher than) the delivery or output' pressure. With an arrangement with at least three cylinders with evenly distributed operating cycles, such as the one shown, there will always be at least one working chamber having the low pressure and at least one having the high pressure. This means that the intermediate sealing chambers 24, 25 and 26, being interconnected by interconnecting ducts 30, will - due to the unavoidable leakage past the various sealing rings - have a pressure somewhere in-between the supply pressure and the delivery pressure. This intermediate pressure is, however, kept close to the supply pressure due to the primary sealing rings 18, 19 and 20 being of the one-way type, i.e. allowing fluid to pass from the Intermediate sealing chamber to the working chamber of the cylinder concerned. Any substantial amount of liquid leaking past the primary sealing ring in a cylinder under high pressure will thus flow through the interconnecting ducts to the intermediate sealing chamber of the nearest cylinder under low pressure and past that cylinder's primary sealing ring into its working chamber, to be pumped along with the remainder of the liquid therein during the next delivery stroke.

Since the pressure in the intermediate sealing chambers is generally at least roughly equal to the supply pressure, the secondary leakage pressure across the secondary sealing rings 21, 22 and 23 will generally be roughly equal to the difference between the supply pressure and the pressure in the external spaces 27, 28 and 29. If the latter are in open communication with the atmosphere, the secondary leakage pressure is roughly equal to the supply pressure, which is usually fairly low and hence causes a minimum of leakage flow. The external space may, however, be connected (in a manner not shown) to the supply side of the pump, in which case the secondary leakage pressure will be practically zero. The secondary sealing rings 21, 22 and 23 will normally - as shown - be of the two- -way type, i.e. sealing against pressure differences in both directions, so as to prevent both the loss of liquid to the surroundings and the ingress of contaminating matter in the system comprising the pump.

Due to the relatively high pressure difference encountered - at least periodically - across the primary sealing rings 18, 19 and 20, these rings have to be held in place by retaining rings 31, 32 and 33. Similar retaining rings (not shown) may also be used to keep yhe secondary sealing rings 21, 22 and 23 in place, but due to the low pressure differences encountered across the secondary sealing rings, such retaining rings will usually not be required.

If the pump only has two cylinders with the two pistons operating in counter-phase, i.e. with one delivering while the other one is filling its cylinder, there is a possibility that at a certain moment in each operating cycle there will not be a low pressure in one of the working chambers at the same time as there is a high pressure in the other working chamber. Such a condition will, however, only prevail during a very small fraction of each operating cycle; hence, the amount of liquid flowing through leakage past the secondary sealing rings will be comparatively small.

Claims

C L A I M S

1. A fluid-displacement machine with at least two cylinders (1;2;3), each with a reciprocating piston (4; 5; 6), in which each piston is sealed in its cylinder by two seals (18, 21; 19, 22; 20, 23) with an intermediate space (24; 25; 28), c h a r a c t e r i z e d in that each intermediate space (24; 25; 26) is in fluid communication (30) with at least one intermediate space (25; 26; 24) associated with one other of said cylinder/piston combinations (2, 5; 3, 6; 1,4).

2. A machine according to claim 1, c h a r a c t er i z e d in that each of the seals (18; 19; 20) lying closest to the working chamber (7; 8; 9) of the cylinder (1;2 3) in question is of the one-way type, allowing fluid to flow past it towards said working chamber.

3. A machine according to claim 1 or 2, c h a r a ct e r i z e d in that it comprises at least three cylinder/piston combinations with at least approximately evenly distributed operating cycles.