US1993721A - Packing - Google Patents

Description

March 5, 1935. R. J. s. PIGOTT 1,993,721

PACKING Filed Jan. 11, 1934 2 Sheets-Sheet 1 March 5, 1935. J, 5, Plea-r1" PACKING 2' Sheets-Sheet 2 Filed ,Jan. 11, 1934 Patented 'ar. i935 PATENT OFFICE 'racxme Reginald J. s. Pigott, Pittsburgh, Pa.-, assignor to Gulf Research & Development Co p ation, Wilmington, Del., a corporation of Delaware Application January 11, 1934, Serial No. 706,265

Claims. (Cl. 1ll3-126) This invention relates to packing; and it comprises in a rotary pump or motor having a rotor rotatably mounted in a stationary casing and adapted to cooperate with a portion of the casing 5 to form a pressure holding chamber, improved packing means for maintaining a pressure .tight seal between the rotor and the casing without excessive binding on the rotor, said means comprising a floating metal packing member engaging the rotor and adapted to be forced there against by pump pressure and a flexible backing member'between the casing and the packing member and adapted to reduce, in regulable amount, the force exerted on the packing member by pump pressure in the pressure chamber, so as to provide a tight packing seal for the pressure chamber without excessive frictional binding; all as more fully hereinafter set forth and as claimed.

In recent years there has been developed a new type of rotary pump comprising a ring gear, with internal teeth, and a cooperating pinion, with external teeth, the combination being mounted in a suitable ported casing and the gears being adapted to be revolved either by the ring gear or by the pinion. The teeth are so designed that the teeth and tooth spaces of the meshing gears form a series of gradually expanding closed chambers during part of a revolution and a series of gradually contracting closed chambers during another part of the'revolution; and the ports are so arranged that .the expanding chambers serve to suck fluid from an inlet and the contracting chambers serve to expel fluid through an outlet.

This type of pump presents many advantages over reciprocating pumps, vane pumps, double pinion pumps and other common designs. The ring-gear-pinion type has high volumetric and mechanical emciency, is simple in design, and can readily be modified for use either as a pump or a gas compressor. It may be used as a motor without change.

In my copending application Serial No. 626,420,

- filed July 30, 1932, I have disclosed particularly advantageous forms of ring-gear-pinion pumps and compressors, in which the expanding chambers draw in fluid for almost a full half revolution, and expel it for almost a half revolution. In

I these pumps the ring gear has one more tooth than the pinion, and the teeth are in continuous sliding contact.

In those pumps the ring gear and the outlet side of the casing cooperate to form a pressure holding chamber, the ring gear and the pressure chamber being sealed off from the rest of the casing and the bearings.. Capillary seals or halffling'devlceswh'ereinthe liquid forming the seal must pursue a meandering course in order to escape, aresatisfactory, in=pumping liquids not 5 excessively thin and at moderate speeds and pressures. These pumps are adapted to develop high pressures (up to several hundred'pounds per square inch in a single pump) and work at high peripheral speeds of the ring gear.

f According to the'present' invention packing means are provided which are adapted to form a tight seal between ring gear and easing under the. conditions of pumping most apt to cause leakage, as when thin (that is, low viscosity) liquids are pumped at high pressures and speeds. My invention comprises a packing member actually making pressure contact with the rotor. In using simple spring rings or floating bands as packers between ring gear and casing it is practically inevitable that thepacker is under full pump discharge pressure, causing it to press heavily on the ring gear when the pump pressures are high. Accordingly, in the use of such packing members, diillculties are met with because of (1) the high peripheral speed, that is, rubbing speed, of the rotor, which tends to produce excessive wear and friction with the packing, and (2) the high pressure in' the pressure chamber in the outlet side of the pump, which tends to force the packing member against the rotor with a pressure which may be as great as 700 or 800 pounds per square inch in high pressure pumping. This pressure is in excess of that required for effecting a tight seal and is too great for as satisfactory bearing conditions. I flnd that in using ordinary cast iron or babbit faced snap rings and sealing strips in sealing the ring gear from the casing, excessive wear and frictional resistance are aptto occur under the extreme pumping conditions described. Soft packings, while satisfactory at moderate pump speeds and pressures, generally fail at high speeds.

I have found that an excellent seal between rotor and casing in high speed, high pressure pumps may be obtained, without substantial frictional resistance and wear, by using a metal packing member mounted in arecess in the casing and in contact with the rotor, forced against the rotor with a moderate, regulable pressure, the pressure used depending upon the discharge pressure of the pump, and being less than the discharge pressure. I utilize the discharge pressure of the pump to force the packing member against the rotor, and I reduce the net pressure of the 65 packing member on the rotor by reducing the fluid pressure on the back of the packing member (against which the pump outlet pressure is exerted). I do this by partially filling up the pressure cavity in the recess between the packing member and the casing, with a flexible partition or dia-- phragm; or by means of a backing filling of soft, readily deformable material of the nature of soft rubber or Thiokol (a synthetic rubber imper-- vious to oils). I can regulate the pressure of the packing member froma small fraction of the outlet pressure, to as near the outlet pressure as desired, by varying the area of the edge 01 the rubber exposed to the fluid pressure; or in the case of the partition, by arranging the partition to cut ofi a greater or less proportion of the packing member from access to pump pressure.

In the accompanying drawings I have shown,

my packing means using a metal packing strip and a rubber filler;

Fig. 2 is a perspective view of the packing means oi. Fig. 1;

Fig. 3 is a view in section along the line A-A 01. Fig. 1; 1

Fig. 4 is a view in section of the pump of Fig. 1 along the line A--A, showing a modified form of the packing means of Fig. 1;

Fig. 5 is a view similar to Fig. 3 showing a modifled form of packing means using a metal diaphragm or partition;

Fig. 6 is a view similar to Fig. 3 of a modified form of packing means using a metal partition unattached to the packing strip; and

Fig. 7 is a sectional view taken along line 3-43 of Fig. 1, the rotor being shown in elevation.

In these showings, in which like reference numerals indicate like parts throughout, Figs. 1 and '7 show in section a gear pump comprising a casing 1 having an inlet 2 and outlet 3. In the casing are mounted ring gear 4 and pinion 5, the gears being parallel and eccentric as shown. Pinion 5 is mounted on a driving shaft 5A. The ring gear has one more tooth than the pinion, and the tooth shapes on the gears are such that the teeth are in continuous sliding contact, forming a series of chambers 6 which expand for half a revolution and contract for te rest of the revolution. The ring gear is provided with ports 6A in communication with the chambers 6. The expanding chambers are in communication with the in-- let through the annular chamber '7, and the contracting chambers are in communication with the outlet through the pressure holding chamber 8. As-the gears turn in the direction indicated by arrows, liquid is taken from the inlet and forced a through the outlet under pressure.

such as crude oil; but such packing means tend to. allow leakage when thin liquids are pumped at high speeds and pressures. Sort packing and plain snap rings or the like are not satisfactory for the reasons given ante.

According to the present invention 1 provide packing means for the ring gear comprising a curved metallic strip 9 fitting the periphery of the ring gear and mounted in a recess 10 in ends of the casing as shown, the thickness of the strip being less than that of the recess. The strip has a slot-like opening 11 as shown equal in size and shape to the opening of pressure holding chamher 8. This strip is made of metal selected. for low frictional resistance and good Wearing qualities, whichmetal may advantageously be nitrided steel, babbitt-faced steel, or Graphalloy (graphite and brass). As shown, this strip engages the outlet side of the ring gear and also extends into the abutments of the casing.

If the strip were used alone, the back of the strip and the recess would be in direct communication with the pressure holding chamber 8, and the full discharge pressure or the pump would be exerted on the strip to force it against the rotor. At high pressures, the strip might be forced against the ring gear with sufiicient iorce to cause seizure; in any case, with excess force over that needed for effecting a seal.

To moderate the pressure of the strip on ends of the rotor, in the embodiment shown in Fig. 1, 1 provide a soft rubber filling 12 in the recess between the strip and the casing. The dimensions of the strip and cavity are such that the area of the edge 13 of the filler is less than the area of the strip. Pressure in the chamber 8 acts only on the edge 14 01 the metal strip and the edge 13 of the filler. The pressure forces the soft rubber to fit the cavity tightly and with a perfect seal all around the edges. The pressure on the back of the sealing strip is reduced in a ratio equal to that of the area 01' the filler to the area or the back of the strip. By changing the ratio or the area of the strip to the edge area or the filler, as by using a thicker strip and a thinner filler, for instance, the pressure exerted by the arcuate sealing strip on the ring gear may be varied as desired. 2

As best shown in Fig. 7 the metal strip 9 completely surroundsthe discharge passage 3 at its boundary adjacent the ring gear 4, the port or opening 11 coinciding with the opening in the discharge passage to afford communication between the chamber 6 and the outlet of the pump.

The filler may be made of other materials than soft rubber, such as Thiokol for instance. The requirement is that the material should be plastic, resilient and impervious and resistant to attack by the fluid being pumped.

In Fig. 4, I have shown a modified form of filler 12' having a cut out slot or groove 15 as shown. This allows access of fluid under pressure to a portion of the filler and hence a greater pressure will be exerted on the sealing strip. This modiflcation is useful when the discharge pressure oi the pump is relatively low. By slotting or grooving the filler the pressure on the sealing strip may be increased without having to increase the thickness of the flller.

In the modification of Fig. 5 a partition or diaphragm i6, advantageously or thin, springy metal, is substituted for the rubber filling. This partition may be likened to a single convolution of a straight edged bellows. It is attached to the strip and to the casing by soldering or brazing as at 17. The partition serves to shut off a portion 0! the area of the back of the sealing strip, thus reducing the net pressure exerted by Pill] hill weaver the strip on the ring gear to a value below the discharge pressure the pump.

In Fig. 6 is shown a modified partition which comprises a thin flexible metallic partition 18 slightly dished as shown, and fastened by riveting or soldering as at 19 to the casing. One edge of the strip simply rests on the sealing strip as shown, and is held tightly thereto by fluid pressure during operation of the pump.

It will be seen that I have provided simple packing means for maintaining a seal between a rotor and stator in a rotary pump. The pressure or the packing means is readily adjustable. My invention is illustrated in its application to a gear pump, but it is useful for effecting seals in similar relations in other devices such as multistage centrifugal pumps, turbines and hydraulic motors, and in rotary pressure devices generally.

What I claim is:

1. In a rotary pressure device having a rotor rotatable in a casing and adapted to cooperate with one portion of the casing to form a pressureholding chamber in communication with an arcuate portion of the periphery of the rotor and with another portion oi the casing to form a separate chamber in communication with another arcuate portion of the periphery of the rotor, improved packing means between the rotor and the first-named portion of the casing com, prising a floating arcuate metallic sealing member engaging the portion of the periphery of the rotor in communication with the pressure holding chamber, the casing being provided with a recess in which the member is positioned, the sealing member being forced against the rotor under fluid pressure from the pressure holding chamber, and means for limiting the area of the sealing member exposed to said pressure, so that the net pressure exerted by the sealing member on the rotor is less than the pressure existing in the pressure holding chamber.

2. In a rotary pressure device having a rotor rotatable in a casing and adapted to cooperate with one portion of the casing to form a pressure holding chamber in communication with an arcuate portion of the periphery of the rotor and with another portion or the casing to form a separate chamber in communication with another arcuate portion of the periphery of the rotor, improved packing means between the rotor and the first-named portion of the casing comprising a floating arcuate metallic sealing strip in contact with the portion of the periphery of the rotor in communication with the pressure holding chamber, the casing being provided with an arcuate recess in which the strip is positioned, the strip being forced against the rotor under fluid pressure from the pressure holding chamber, and means ror limiting the pressure on the back of the strip to reduce the pressure of the strip against the rotor, said means comprising flexible means in the recess in contact with the strip and the casing and adapted to close off a portion of the area of the back of the strip from the direct pressure of the pressure chamber.

3. The packing means of claim 2 wherein the means for reducing the sealing strip pressure comprises an arcuate rubber filling in the recess between the strip and the casing, the area of the edge of the filling being presented to the pressure in the pressure holding chamber and this area being less than the area of the back of the sealing strip whereby the pressure on the sealing strip is reduced in inverse ratio to said areas.

4. The packing'means of claim 2 wherein the means for reducing the sealing strip pressure comprises a rubber filling in the recess between the strip and the casing, the filling having a slot in its edge open to fluid pressure in the chamber, the slot extending only part way through the filling, so that the pressure on the sealing strip is less than the fluid pressure. I

5. The packing means of claim 2 wherein the means for reducing the sealing strip pressure comprises an arcuate, flemble, thin metallic diaphragm in the recess between the strip and the casing, the diaphragm being in contact with the casing and the strip and being adapted to shut off a portion of the area of the strip from access to the pressure in the pressure holding chamber. 6. The packing means of claim 2 wherein the means for reducing the sealing strip pressure comprises an arcuate, flexible, thin, folded metallic diaphragm in the recess between the strip and the casing and attached to the strip and to the casing, and being adapted to shut 0d a portion of the area of the strip from access to the pressure in the pressure holding chamber.

'1. The packing means of claim 2 wherein the means for reducing the sealing strip pressure comprises an arcuate, thin, flexible metallic diaphragm in the recess between the strip and the casing, attached to the casing and resting on the strip, and being adapted to shut off a portion of the area of the strip from access to the pressure in the pressure holding chamber.

8. An improved rotary pressure device comprising a pumping rotor, a stator provided with a chamber extending arcuately over a portion of the periphery of the rotor, a pressure holding chamber extending arcuately over another portion of the periphery of the rotor and provided with an arcuate recess in the pressure holding chamber adjacent the periphery of the rotor, said recess terminating in an abutment at each end,

the abutments separating and defining the said enclosing the pumping rotor and provided with.

a chamber extending arcuately over a portion of the periphery of the rotor, a pressure holding chamber extending arcuately over another portion or the periphery of the rotor and provided with and having an arcuate recess adjacent the periphery of the rotor at each end thereof, an arcuate packing member in the recess and engaging the peripheral end portions of the rotor and provided with a slot-like opening registering with the middle portion of the rotor, and a similarly shaped yieldable backing member having a slotlike opening registering with the opening in said packing member, the backing member being positioned in the recess between the packing memher and the stator and forming a seal between between the rotor and the casing comprising a ported metallic sealing member surrounding said fluid passage at the'boundary adjacent the rotor, the casing being provided with a recess in which the member is positioned, the back of the sealing member being in communication with fluid pressure from the passage so that said pressure acts to hold the sealing member against the rotor and a member for variably limiting the area of the back of the sealing member exposed to said pressure so that the net pressure exerted by the sealing member on the rotor may be reduced in controlled amounts under:the pressure existing in 5 said fluid passage.

REGINALD J. S. PIGO'I'I.

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