GB2072055A - Self-cleaning centrifugal separator - Google Patents

Abstract

A self-cleaning centrifugal separator comprises an axially movable piston-type slide valve (3) for performing partial or total discharges from the separator drum (2,7). A closing chamber (8) for the valve is sealed by a gasket (10) between the valve and the adjacent drum part (7). The gasket in the closed position of the valve is subjected on one side to the action of liquid pressure in the closing chamber and on the other side to atmosphere. The gasket (10) is arranged in a recess (9) provided in the slide valve on the closing chamber side. The gap between the radially internal surface of the gasket and the slide valve is smaller than the gap between the bottom of the gasket and the adjacent drum part (7) when the valve is in the fully open position. <IMAGE>

Description

SPECIFICATION A self-cleaning centrifugal separator The invention relates to a self-cleaning centrifugal separator having a gasket arrangement in the centrifugal drum, the centrifugal drum having an axially movable piston-type slide valve for performing partial or total discharges and which has one or more closing chambers. The closing chamber is sealed by at least one gasket on the piston-type slide valve and on the adjacent drum part, whilst when the valve is in the closed position the gasket is on one side subject to the action of the liquid pressure in the closing chamber and on the other side is connected to atmosphere.

A centrifugal drum with such a gasket arrangement is, for example, known from German Patent 20 41 371. The centrifugal drum has a closing chamber positioned below the piston-tye slide valve and said chamber is sealed with respect to the atmosphere by a gasket arranged on the valve periphery. Within the piston-type slide valve the gasket is embedded in a slot surrounding all sides of the said gasket. The gasket seals the closing chamber relative to the atmosphere during operation under the action of the centrifugal force and the liquid pressure in the closing chamber. During the axial movement of the piston-type slide valve the gasket is guided and carried along in the slot at the time of the partial or total discharges.

German Patent 20 48429 discloses a centrifugal drum having an inner and an outer closing chamber outside the piston-type slide valve and each chamber is sealed by a gasket arranged in said valve.

The gaskets used in such centrifugal drums equipped with piston-type slide valves are generally made from an elastic sealing material, e.g. rubber, no particular difficulties being encountered when fitting such gaskets into the slot. However, such elastic gaskets are not suitable for certain liquids which are to be separated or clarified in the centrifuges and which can come into contact with the gasket. This is particularly the case if the centrifugal drum has to be operated at high temperatures. The gaskets often tend to swell or are destroyed by chemical or thermal influences. It is therefore always necessary to use gaskets adapted to the product of the separating temperature. Such gaskets are frequently only slightly elastic or are inelastic, such as e.g. in the case of polyamide or PTFE gasket types.Serious difficulties are encountered in fitting such gaskets into the slots due to their limited expansibility or elasticity and fitting may even prove impossible. In addition, a relatively large amount of work is connected with the production of this slot in the piston-type slide valve.

The problem of the present invention is to so arrange the gasket for sealing the closing chamber relative to atmosphere in the centrifugal drums of automatically discharging centrifuges that it is even possible to easily fit less elastic gaskets.

According to the present invention self-cleaning separator comprises an axially moveable pistontype slide valve for performing partial or total discharges and having a closing chamber sealed by a gasket between the piston-type slide valve and the adjacent drum part the gasket in the closed position of the valve being subjected on one side to the action of the liquid pressure in the closing chamber and on the other side to atmosphere, a recess for receiving the gasket being provided in the piston-type slide valve on the closing chamber side and the liquid gap between the internal diameter of the gasket and the slide valve being smaller than the minimum size liquid gap between the bottom of the gasket and the adjacent drum part.

As a result of this gasket arrangement and the construction of the piston-type slide valve it is possible to use any type of gasket, because there is no longer any need to stretch the latter for fitting purposes. In addition, the manufacture of such a recess is much cheaper than that of grooves or slots.

As the sealing of the closing chamber by the gasket is only ensured if said gasket is pressed in front of the gap between the piston-type slide valve and the adjacent drum part by the liquid pressure prevailing in the closing chamber, the liquid pressure below the gasket must always be higher than that above it. This is ensured by the fact that on filling the closing chamber with liquid the liquid pressure firstly builds up below the gasket, so that the liquid gap below the gasket must be larger than the gap between the piston-type slide valve and the internal diameter of the gasket. The small gap acts as a constriction.

According to a special embodiment a shoulder is provided in the drum part for supporting the gasket in the lowermost position, so that there is a larger liquid gap between the drum part and the gasket than that between the piston-type slide valve and the gasket internal diameter.

According to another embodiment recesses are provided in the drum part which are higher than the liquid gap between the piston-type slide valve and the gasket internal diameter.

An embodiment of the invention is described hereinafter relative to the drawings, wherein show: Figure 1 a centrifugal drum in the operating state, the gasket being forced into the upper sealing position in the closed position of the piston-type slide valve by the liquid pressure prevailing in the closing member.

Figure 2 a larger-scale cutout of Figure 1 in the non-operational state, the gasket being in the lowermost position on a shoulder in the drum part.

Figure 3 a larger-scale cutout of Figure 1 in the non-operational position, the gasket being in the lowermost position on recesses in the drum part.

In Figure 1 the dirt-holding space 1 in the centrifugal drum is bounded at the top by a drum cover 2 and at the bottom by a piston-type slide valve 3 which, during its axial movements opens and closes the ejection openings 4forthe solids collected in the dirt holding space. The separating chamber of the centrifugal drum is substantially formed by the disc stack 5 located therein and in it clarification or separation takes place of the liquid material supplied to the drum by means of ducts 6. The closing chamber 8 is positioned between slide valve 3 and the adjacent drum part 7. Closing chamber 8 is sealed with respect to the adjacent drum part 7 by a gasket 10 arranged in a recess 9 in the slide valve.

Discharge ducts 11, controlled by discharge valves 12, pass out of the outer end of the closing chamber.

The discharge valves can, for example, be held in the closed position by a permanent liquid supply via ducts 13 and can be brought into the open position by blocking the liquid supply.

In perse known manner the liquid supply takes place by means of a coliecting channel 14 from which firstly the discharge valve 12 is brought into the closed position by the duct 15 emanating from the radially outer end of the channel via duct 13 and following the filling of said ducts the closing fluid passes through duct 16 into closing chamber 8, so that the piston-type slide valve 3 is brought into the closed position. Due to the liquid pressure in the closing chamber and under the action of the centrifugal force on gasket 10 the latter seals in recess 10 of slide valve 3 the gap 17 between the latter and the adjacent drum part, which is connected to atmosphere via the ejection opening 4.

The closing liquid supply is blocked for dirt ejection purposes. As a result the discharge valve 12 is opened and allows the closing liquid to drain from the closing chamber 8. Under the action of the overpressure in the separating chamber and whilst carrying with it gasket 10 slide valve 3 moves into the lower position. As a result between slide valve 3 and drum cover 2 the drum filling is ejected.

After filling the closing chamber 8 with closing liquid the piston-type slide valve 3 is returned to the closed position. To ensure that gasket 10 does not remain in its lower position during this closing process (Figure 2) and is also moved into the upper sealing position, on filling the closing chamber 8 with closing liquid the liquid pressure below the gasket must be higher than that above it. Since according to the invention the liquid gap 18 between slide valve 3 and the internal diameter of the gasket 10 is smaller than the liquid gap 19 between the gasket and the adjacent drum 7, gap 18 acts as a constriction, so that initially the larger liquid quantity collects below the gasket, so that the liquid pressure is higher below the gasket than above it and the latter is consequently pressed into the upper position against the slide valve.To ensure that the liquid gap 19 is maintained, a shoulder 20 is provided in drum part 7 and limits the lower position of the gasket.

Figure 3 shows another embodiment in which the liquid gap 21 between gasket 10 and drum part 7 is formed by recesses 22 in the drum part, whose height is greater than the gap 18 between slide valve 3 and gasket 10.

After assembling the centrifugal drum, e.g. following cleaning, the gasket will remain in the lower position, as shown in Figures 2 and 3. Only after filling the chamber 8 with liquid will the gasket seal gap 17 with respect to the atmosphere.

It is also conceivable for the discharge duct 11 emanating from closing chamber 8 to be arranged on a smaller diameter than the internal diameter of gasket 10, so that during the discharging processes the liquid pressure below the gasket is maintained.

However, when the drum is stationary the closing liquid will still escape from the drum so that the gasket 10 can drop into the lower position. The arrangement of such a gasket can naturally be used for all the movable drum parts of centrifuges which are under liquid pressure and are to be sealed.

Claims (4)

1. A self-cleaning centrifugal separator comprising an axially movable piston-type slide valve for performing partial or total discharges, and having a closing chamber sealed by a gasket between the piston-type slide valve and the adjacent drum part, the gasket in the closed position of the valve being subjected on one side to the action of the liquid pressure in the closing chamber and on the other side to atmosphere, a recess for receiving the gasket being provided in the piston-type slide valve on the closing chamber side and the liquid gap between zE e internal diameter of the gasket and the slide valve being smaller than the minimum size liquid gap between the bottom of the gasket and the adjacent drum part.

2. A self-cleaning separator as claimed in claim in which the liquid pressure is limited by a shoulder provided on the drum part.

3. A self-cleaning centrifugal separator as claimed in claim 1 in which the liquid gap is formed by recesses on the drum part.

4. A self-cleaning centrifugal separator substantially as described hereinbefore with reference to and as shown in the accompanying drawings.