US878528A - Rotary pump for gases. - Google Patents

Description

\ f: E r i i E E A PATENTED FEB. 11, 1908.

0. HOFFM'ANN. ROTARY PUMP FOR GASES. 4

APPLICATION FILED JUNE 9, 1906.

m u omus PKTERS C uNIT STATES PATENT CARL HO FFMANN, OF CHARLOTTENBURG, GERMANY, ASSIGNOR TO SIEMENS-SOHUCKERT- connecting pipe penetrate WERKE, GESELLSGHAFT MIT BEscHRIiNK'rER ROTARY PUMP FOR cases.

HAFTUNG, OF BERLIN, GERMANY.

Patented Feb. 11, 1908.

-Application filed June 9. 1906- Serial No. 321.006-

To all whom it may concern:

Be it known that I, CARL HOFFMANN, engineer, a subject of the German Em eror, residing at Charlottenburg, near Ber in, Germany, have invented a certain new and useful Improvement in Rotary Pumps for Gases, of which the following is a full, clear, concise, and exact description.

In the case of air pumps which are intended to produce a very intense vacuum the packing of the sliding members is effected by means of liquids, such as oil, mercury and so on, which do not volatilize easily. In particular rotary pumps for the aforesaid purpose-must be constructed as so-called wet pumps as the difficulties in packing their sliding members can be effected only by means of ample quantities of liquid which between the sliding members.

uchji .1'9tary pump for producing an in:

tense vacuum is shown in vertical section me ac'coriipanvmg drawing in which a indicates'the rotatiiig'cylinder which is supported e ccentrically with regard to the pumpchamber and which in a well-known manner by means of the two vanes f, f, sliding in said cylinder, draws in the gas through the h from the space to be exhausted and forces it at a higher pressure into the receiver 1'. This receiver may be connected with an auxiliary pump but this arrangement is irrelevant for the purpose of the subsequent description. Now in order to be able to u e the packing liquid, as which in this case oil is most used, the suctionport s and the delivery-port d-of the ump, as is shown in the drawing are suitab y arrangedabove, and an ample quantity, of oil is kept above'd. In the positions of the vanes as shown in the drawing, oil can then always. get readily to the sliding surfaces, while on the other hand the oil adhering to the cylinder and to the vanes cannot pass into the suction-port. Now in the case of such rotary vacuum pumps a special check valve is preferably arranged in front of the deliveryport at, not so much" in order to improve the packing of the whole pump as to avoid loss of energy during operation. For instance, if such a non-return valve were not-employed, when one of the vanes has passed the edge 7c of the delivery-port d the gas under the higher pressure in the receiver 1 would brush into the pump-chamber so placed in f ee communication with said receiver, or in other Words the vanes would have to work for the greater part of their stroke against the higher pres sure in the receiver 1'. This is manifestly avoided by a special non-return valve in front of the delivery-port d, which valve does not open until the pressure behind it is equal to that in the receiver 7.

On account of principles generally recognized in the construction of pumps the clearance space under the non-return valve has hitherto been made as small as possible but in consequence of this construction difficulties have arisen in the use of liquid packing. According to experience oil, which is otherwise very serviceable for the aforesaid purpose, sufl'ers from the defect'that the pumpparts during action cause it to form foam,

t. e. bubbles, both small ones and those of the most minute size, surrounded with a film of oil are formed. If now such bubbles during the rotation of the cylinder 0 by adhering to I the latter reach the suction side of the pump they expand in correspondence with the difference of pressure, and as under some circumstances the va. uum to be produced amounts to only a small fraction of amillia fairly large chamber is arranged which must no longer be designated a clef rance. space and which suitably should amou at to not less than 10% of the stroke-volume of the pump. On account of the provision of such a chamber having a sufficient size the bub- 1 bles, as experience has shown, have opportunities to rise up in the homogeneous mass of oil on account of their buoyancy, whereas if a chamber which is too small is provided said chamber remains filled with foam. The aforesaid fairly large chamber is on the other I hand principally filled with homogeneous oil I and the air bubbles pass quickly through the valve 1) to the surface of the oil in the re ceiver 1 where they quickly vanish. In the case of this method of working the quantity of oil in the aforesaid chamber must of course diminish more and more. In order to supply the place of the oil which has passed through the check valve together with the bubbles a small opening is provided in the casing w containing said chamber at a place which oil-foam cannot readily reach, said opening permitting oil which is freed from foam to flow back into said chamber under the action of the pressure in 1" which on the average is greater than that in said chamber. This connecting-opening is most simply and suitably in the form of a fine chink or gap which remains between the body ofthe pump and the casing w when the latter is screwed on the former.

The above-described arrangement is of course a plicable to rotary pumps of other forms W 'ch are intended to be utilized for similar urposes. Also it is not limited to pumps or producing an intense vacuum but can in suitable cases be employed with advantage for any rotary pumps pumping gas. What I claim as my invention and desire to secure by Letters Patent, is:

1. A rotary pump for gases, comprising in combination, a pump chamber casing, hav

ing an inlet port suitably located and a relatively Wide delivery port above, rotary means in the pump chamber for propelling gas therefrom to said delivery port, means for supplying a liquid packing, an intermediate casing forming a relatively wide chamber between and communicating with the dclivery port below and the packing supplying means, a check valve in the upper portion of said intermediate casing adapted to permit escape of packing containing bubbles, and means for admitting packing free from bubbles into the lower portion of the chamber within said intermediate casing substantially equal in quantity to that escaping through said check valve.

2. A rotary pump for gases, comprising in combination, a pump casing having an inlet port suitably located and a delivery port above, rotary means in the pump chamber for propelling gas therefrom to said delivery port, a receptacle located above said delivery port and adapted to contain packing liquid, an intermediate casing forming a chamber between and communicating with the delivery port below and the packing liquid vessel above said intermediate casing having a volume equal to at least ten per cent. of the stroke volume of the pump, a check valve in the upper portion of said intermediate casing adapted to permit escape of packing containing bubbles and means for admitting packing freefrom bubbles into the lower portion of the chamber, within said intermediate casing substantially equal in quantity to that escaping through said check valve.

In witness whereof, I hereunto subscribe my name this 22nd day of May A. D., 1906.

I CARL HOFFMANN. l/Vitnesses l'lENRY HAsPEn,

VVOLDEMAJL IEIAUPT.

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