GB2047341A - Centrifugal Pumps - Google Patents

Abstract

The pump outlet has an opening 21 of substantially rectangular cross- section from which extends a tangential outlet pipe 19 having a substantially rectangular cross-section over the main portion of its length. At a distance from the opening, the pipe is provided over a limited portion 22 of its length with a pipe section exhibiting a cross-sectional change from substantially rectangular to circular permitting coupling to a discharge pipe 20 of circular cross- section. <IMAGE>

Description

SPECIFICATION Centrifugal Pumps This invention relates to centrifugal pumps comprising a pump housing having an inlet disposed coaxially of the main axis of the pump and an outlet disposed substantially tangentially relative to the pheripheral wall of the pump housing.

It has been usual in centrifugal pumps to utilise an oval outlet opening from the pump housing to an adjacent discharge union which is made with a circular cross-section. Practical measurements have shown that significant friction occurs in the flow of pump medium from the pump housing to the discharge union just by the outlet opening. This friction in the flow of pump medium can be determined audibly in the form of a high noise level.

With the present invention the aim is to obtain a reduction of the friction in the flow of pump medium from the pump housing to the discharge union.

According to the present invention a centrifugal pump comprises a pump housing having an inlet disposed coaxially of the main axis of said pump and an outlet disposed substantially tangentially relative to the peripheral wall of the pump housing, said outlet having an opening of substantially rectangular cross-section from which extends an outlet pipe having a substantially rectangular crosssection over the main portion of its length, said pipe being provided at a distance from said opening in a limited portion of its length with a pipe section exhibiting a cross-sectional change from substantially rectangular to substantially circular enabling coupling to a discharge pipe of circular cross-section.

It can be ascertained audibly that, with the solution according to the invention, there is obtained a lower noise level at the outlet opening from the pump housing than with known solutions. Practical measurements have also shown that reduced friction is achieved with the solution according to the invention.

It is preferred that the pump housing and the outlet pipe are made of drawn sheet metal members which are welded into a coherent construction, the outlet pipe being made of two longitudinally divided pipe half sections, while the main portion of the pump housing is made in one piece.

In this way, the outlet pipe and the main portion of the pump housing can be made separately with a most favorable possible shape for their respective purposes by means of a relatively simple manufacturing operation based on the drawing of pre-adapted sheet metal members. After drawing the main portion of the pump housing, the substantially rectangular outlet opening in the peripheral wall of the pump housing can be stamped in an easy manner, while the pipe half sections which are to form the outlet pipe, can be formed in a correspondingly simple manner with said substantially rectangular or substantially quadratic cross-section over a desired portion of the length of the pipe and with a transition to a circular cross-section at the end of the pipe where it is to be connected to a discharge pipe of circular cross-section.After effecting welding, there can be obtained a pump housing with associated outlet pipe which does not require extra machine working or, at any rate, requires minimal subsequent treatment after final welding.

In order that the invention can be more clearly understood, a convenient embodiment thereof will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1-3 shows a pump housing in end view, side sectional view and plan view respectively.

Fig. 4-6 shows different members from which the pump housing is made.

Referring to Figs. 1 to 3, a pump housing comprises a main portion 10 internally defining a hollow space 11 which receives a pump rotor (not shown further) and which forms the pump chamberperse together with the passage of the pump housing. In one end of the pump housing, there is shown an inlet union 12 for coupling to a suction pipe or a suction connection piece 13, while in the opposite end.

of the pump housing there is a fastening union 14 for fastening in a packing box 1 5 with associated holder 16. The fastening union 14 is further provided with a fastening flange 17 for coupling to a similar flange on a pump motor. From the peripheral wall 18 of the pump housing, there extends tangentially outwards an outlet pipe 1 9 which is adapted to be coupled to a discharge pipe 20 of circular cross-section.

There is employed an outlet pipe 1 9 from the pump housing, where minimal friction for the pump medium can be achieved in the transition portion between the pump chamber of the pump housing and the inlet to the outlet pipe 19 and in the outlet pipe per se. Provision is made for a substantially rectangular outlet opening 21 in the peripheral wall 1 8 of the pump housing (see Fig. 4), so that the pump medium, which is imparted a forward displacement with a substantially rectangular crosssection in the pump housing, can be led further outwards from the pump housing via the outlet opening 21 in a tangential direction relative to the pump housing with a similar rectangular cross-section.

Furthermore, provision is also made for the outlet pipe 19, at any rate over a portion of its length, reckoned from the opening 21, to have a similar rectangular cross-section. At the discharge end of the outlet pipe 19, the outlet pipe is designed with a transition portion 22 where the pipe passes gradually over from a substantially rectangular cross-section into a circular cross-section. By arranging this transition portion 22 at a certain distance from the opening 21 and, at the same time, providing for a uniform transition from the rectangular to the circular cross-section, the friction of the pump medium has been reduced to a significant degree in the transition between the pump housing 10 and the discharge pipe 20.

In Fig. 4 there is shown a member 23 which is made by drawing an annular metal sheet into a double curved main portion 10 for the pump housing. After the drawing operation, there is effected stamping of the opening 21 in the peripheral wall 18 of the pump housing together with the bored or pressed holes for the fastening bolts in the fastening flange 1 7.

In Fig. 5 and 6, there are shown two pipe half sections 24 and 25 which are made from their respective sheet metal members and drawn to the shape shown. After welding together the pipe half sections into a coherent outlet pipe 19, this is welded to the pump housing at the opening 21 and there is welded on an end union 26 for coupling together the outlet pipe 19 and the discharge pipe 20.

Similarly, an end union 27 is welded on for coupling together the pump housing with a suction conduit 13. Internally in the pump housing, there is welded on the packing box 1 5 with associated holder 1 6 since it is also preferable to use a packing box and a holder which are made separately by drawing out from the sheet metal material. After welding together the aforementioned members, the pump housing is ready for use since further machine working or after finishing of the pump housing is not required.

In addition to fabricating the pump housing from metal sheets in the manner previously described, the main cover portion of the pump housing, excluding the packing box and holder, can be made by an alternative procedure which involves subjecting synthetic thermoplastics materials, optionally reinforced, to injection moulding. It will be appreciated that when transparent plastics materials are employed for the pump housing, visual control of the interior of the pump is then possible. Preferred synthetic thermoplastics materials are supplied by Hoechst A.G. under the registered Trade Marks "Hostaform" and "Hostalen PP".

"Hostaform" is manufactured by copolymerising trioxane (a cyclic trimer of formaldehyde) with a smaller quantity of a comonomer, for example, a cyclic ether or cyclic formaldehyde. By the cationic polymerization of the starting materials, linear macromolecules are synthesised whose chains consisting predominantly of oxymethylene units of the formula -CH2O- are modified by means of statistically distributed units having C-C bonds. The linear structure and high degree of crystallinity of these acetal copolymers determines their good physical properties.

0 catalyst H2 CH,+X---1HO-Y[(CH,O),-Y]-CH,-O-Y-H I I 0 0 CH2 X=a cyclic ether or cyclic formaldehyde (for example).

Y= an oxyalkylene group with two or more vicinal carbon atoms (for example).

"Hostalen PP" is an isotactic polypropylene of high crystallinity manufactured with the assistance of stereo-specific catalysts according to Ziegler/Natta. By means of stereo-regulated copolymerization of propylene with lower L olefins, preferably ethylene, Hostalen PP type materials can be made which exhibit modified properties compared with the homopolymers.

It has been found especially desirable to employ substantially cylindrical pump housings, that is to say housings with substantially straight peripheral walls of cylindrical shape. With such housings, there is obtained the most favorable rectangular outlet opening. By making the peripheral walls of the pump housing somewhat curved in an axial direction, the rectangular outlet opening has correspondingly curved edges at opposite end edges of the outlet opening. Such a solution is less desirable since it produces greater friction.

The utilisation of a cylindrical peripheral wall with an outlet which is both rectangular and tangential with respect to the pump housing minimises the friction in the transition from the housing to the rectangular outlet pipe since the pump medium can be displaced outwards from the pump housing without a change in shape taking place of the flow of pump medium. It is important that the change in shape of the flow of pump medium occurs gradually in the outlet pipe at a distance from the outlet opening of the pump housing. It is clear that the rectangular pipe has a certain axial dimension and an increasing rectangular cross-section in an axial direction. Consequently, there is also obtained an increasing cross-section in the transition between the rectangular and circular cross-sections. In the outlet pipe,, there is present a certain ejector effect (Venturi effect) as a result of the increase in crosssection. By increasing the cross-section and altering the shape of the flow of medium, friction problems are largely avoided as demonstrated by an especially low noise level. As a consequence of pressure changes in the discharge pipe at a distance from the pump housing, a favorable ejector effect is obtained. The ejector effect is particularly useful in connection with the pumping of foam- or aircontaining pump media. In this particular area, the centrifugal pumps of the present invention have shown themselves to be exceptional.

With one and the same standard pump housing, it is possible to employ the same housing for pumps of different pump capacity and with a high degree of efficiency in each individual case, by solely altering the diameter of the inlet opening to the pump housing in addition to changing the power of the drive motor.

Claims (3)

Claims

1. A centrifugal pump which comprises a pump housing having an inlet disposed coaxially of the main axis of said pump and an outlet disposed substantially tangentially relative to the peripheral wall of the pump housing, said outlet having an opening of substantially rectangular cross-section from which extends an outlet pipe having a substantially rectangular cross-section over the main portion of its length, said pipe being provided at a distance from said opening in a limited portion of its length with a pipe section exhibiting a cross-sectional change from substantially rectangularto substantially circular enabling coupling to a discharge pipe of circular cross-section.

2. The pump according to Claim 1 , wherein the pump housing and the outlet pipe are made of drawn sheet metal members welded together into a coherent construction, said outlet pipe being fabriated from two longitudinally divided pipe half sections while the main portion of the pump housing is of unitary construction.

3. Centrifugal pumps as claimed in Claim 1 and substantially as described herein with particular reference to Figs. 1-3 of the accompanying drawings.