GB2023739A

GB2023739A - Rotary positive-displacement fluid-machines

Info

Publication number: GB2023739A
Application number: GB7921620A
Authority: GB
Original assignee: Allweiler AG
Current assignee: Allweiler GmbH
Priority date: 1978-06-28
Filing date: 1979-06-21
Publication date: 1980-01-03
Also published as: DE2828348A1; GB2023739B; CH641250A5; FR2429909A1; FR2429909B1

Abstract

In an externally-meshing screw machine, which may be a pump (as shown), a main screw 2 meshes with an idler screw(s) 3, 4 and the axial thrust on the latter is balanced by fluid pressure on a pin(s) 20, 21 in a sleeve(s) 22, 23 with sufficient radial clearance relative to the housing 1 to render it self-aligning with respect to the pin(s). <IMAGE>

Description

SPECIFICATION Screw spindle machine The object of invention is a screw spindle machine with a drive spindle and at least one driven spindle, the driven spindle having a pin at the low pressure side for compensating for the axial thrust which is enclosed with a narrow drive clearance by a sleeve and is acted upon by hydraulic fluid.

In known screw spindle machines of this type the sleeves with the driven spindles serving to compensate for the axial thrust are centred in alignment in the pump housing and at the same time are firmly clamped axially.

This arrangement is manufacture-intensive and therefore expensive and in addition it can be realized economically only on cast pump housings. This arrangement is for example difficult to realize in pump housings manufactured by continuous casting or machined from solid material since, between the beginning of the delivery region of the spindles and the devices to centre the sleeves in alignment with the driven spindles, large chambers and channels are necessary for conducting fluid and these can be produced only by machining.

These disadvantages are in fact avoided by arrangements known for example from Allweiler screw spindle pumps of the SSH range in which the sleeves serving for thrust compensation are placed loosely on the driven spindles. However, as a result of suction difficulties when the pump is started up these arrangements are not advantageous with pumps having low discharge rates. As a result of lacing the sleeves loosely and of the necessary axial clearances present, a great quantity of air is constantly circulated inside the pump during the suction action of an empty pump.

Especially with small pumps, this circulated volume of air can correspond to the discharge capacity of the pump so that no fluid at all is drawn off or fluid is not drawn off for too long a period and as a result of dry operation the pump soon becomes damaged.

The underlying object of the invention is to provide an arrangement of the sleeves arranged on the pins of the driven spindles on screw spindle pumps of the initially mentioned type so that reliable suction is guaranteed even with small machines and so that at the same time the pump can be manufactured economically.

To this end it is proposed according to the invention that the sleeve is placed on the driven spindle with allround radial clearance relative to the surrounding pump housing and is inserted only under slight axial prestressing of an elastomeric ring between a collar of the pump housing and the suction-side pump cover, the internal diameter of the collar being greater than the external spacing of the driven spindles.

This construction of the screw spindle machine according to the invention has the advantage that the sleeves do not have to be fitted into the housing in any particular manner as they are self-centering when fitted by being placed on the driven spindles and also later during operation they may still be slightly displaced if required, limited by the slight axial prestressing. The axial prestressing also prevents the sleeve rising from its position on the pump cover when the pump is started up. This prevents air being pumped round in greater quantities. The arrangement of the sleeves may therefore also be used for pumps having smaller discharge rates. Furthermore, as the sleeves are fixed axially on a diameter outside the spindles only by a collar, it is not difficult to provide channels in the pump.It is therefore also possible without great manufacturing costs to use continuous cast pump housings or pump housings made of solid material with the construction of the screw spindle machine according to the invention.

The elastomeric ring is preferably a sealing ring which is partially inserted into a groove on the pump cover or the sleeve and which serves to seal the fluid supply to the inside of the sleeve.

In this way the function of the prestressing of the sleeve is connected in a simple manner with the sealing of the sleeve which is so important for the suction action.

In the case of a pump with two opposed driven spindles, the sleeves preferably consist of two equal semi-circular plates, together forming a circle, in which the bores are made for receiving the pins of the driven spindles.

This construction makes it possible for the sleeves to be manufactured from a simple disc which is divided into two equal parts before or after the bores are made. For mounting the sleeves or the two semi-circular plates respectively in the pump housing therefore, a normal cylindrical recess is sufficient which does not need to be fitted exactly, as a result of the wide radial clearances between the sleeves and the housing.

The provisions according to the invention thus result in a particularly simply constructed and reliably operating machine.

A screw spindle machine constructed according to the invention is represented in the drawing: Figure 1 shows a longitudinal section through the screw spindle machine, Figure 2 shows a cross section at the level of the sleeves on the low pressure side along the line A-B shown in Fig. 1.

In the screw spindle machine a drive spindle 2 and two opposed driven spindles 3 and 4 are rotatably mounted in the housing 1.

When the machine is operated as a pump, fluid is drawn from the low pressure chamber 5 into the high pressure chamber 6 when the pump is operated with clockwise rotation, the fluid being conducted via the intake connecting pipe 7, merely shown schematically, and passed on via the pressure connecting pipe 8 also shown only schematically. The drive spindle 2 is mounted at the pressure side by means of a shaft collar 9 in a sleeve 10. By means of a shoulder 11 the shaft collar 9 abuts on the one hand the front face 1 2 of the sleeve 10 and on the other hand a front face 13, provided with grooves, of the pressure-side pump cover 14 which is screwed onto the pump housing 1 by means of screws 1 5. By means of this arrangement, the drive spindle is mounted radially at the pressure side and axially.The shaft seal 1 6 is also arranged in the pump cover 1 4. The chamber 1 7 between the shaft collar 9 and the shaft seal 1 6 is connected via the bores 18, 1 9 with the low pressure chamber and thus is relieved of the discharge pressure. It is therefore possible by means of the specific sizing of the shaft collar 9 to relieve the drive spindle 2 of the axial thrust.

The driven spindles 3 and 4 are provided at the low pressure side with pins 20 and 21 which are enclosed with a narrow drive clearance by the sleeves 22 and 23. As can be seen in particular from Fig. 2, the sleeves have a semi-circular cross section and are inserted with allround radial clearance 24 into a cylindrical recess 25 of the pump housing 1. No radial centering of the sleeves is therefore necessary; they align themselves automatically to the driven spindles when they are inserted. The sleeves are fixed axially by the collar 26 attached on the pump housing 1 which has a greater diameter than the spacing of the two driven spindles and by the pump cover 27 on the low pressure side which is screwed by means of screws 28 onto the pump housing 1.The distance between the pump cover 27 and the collar 26 is somewhat greater than the thickness of the intermediate part of the sleeves 22 and 23. A groove 29 and 30 into which an elastomeric ring is placed, more particularly a collar of a thickness somewhat greater than the depth of the groove, is provided in the sleeves 22 and 23.

After assembly this produces a slight prestressing by means of which the sleeves 22 and 23 are pressed against the collar 26 of the housing 1. The prestressing is chosen so that it is still possible to align the sleeves radially, for example after assembly when the machine has been started up. At the same time the elastomeric ring seals the fluid supply to the inside of the sleeves 22 and 23 which is effected via the bores 31, 32, 33, 34 and 35 from the high pressure side of the machine. The diameters of the pins 20 and 21 are or may be selected so that the axial forces on the driven spindles are compensated for by the pressure load in the sleeve.

Claims

1. Screw spindle machine having a drive spindle and at least one driven spindle, the driven spindle having a pin to compensate for the axial thrust at the low pressure side which is enclosed with a narrow drive clearance by a sleeve and is acted upon by hydraulic fluid, characterised in that the sleeve is placed onto the driven spindle with an allround radial clearance relative to the surrounding pump housing and is inserted under the slight axial prestressing of an elastomeric ring between a collar of the pump housing and the low pressure side pump cover, the internal diameter of the collar being greater than the external spacing of the driven spindles.

2. Screw spindle machine according to Claim 1, characterised in that the elastomeric ring is a sealing ring partially inserted into a groove on the cover of the pump or the sleeve and serving to seal the fluid supply to the interior of the sleeve.

3. Screw spindle machine according to Claim 1 or 2, characterised in that in the case of a machine with two opposed driven spindles the sleeves consist of two equal semicircular plates, which together form a circle, in which the bores are made for receiving the pins of the driven spindles.