US2044867A - Regulating device for vacuum pumps - Google Patents

Description

Patented June 23, 1936 PATENT OFFICE BEGULATING DEVICE FOR VACUUM PUMPS George H. Woodard, Phillipsburg, N. J., assignor to Ingersoll-Band Company, Jersey City, N. J., a corporation of New Jersey Application June 1, 1934, Serial No. 728,491

This invention relates to pumps, and especially to a regulating device to be connected to pumps for exhausting an enclosed space to establish a vacuum therein. 5 An object of the invention is to provide a pump which will not require a disproportionatelylarge 'quantity of power to operate it when the work of creating the vacuum is first commenced.

When a vacuum pump, particularly of the ro- 10 tary type, is connected, for example, to a closed vessel, such as a condenser in which steam or other vapor is to be liquefied, so as to put the condenser ,into condition for use by drawing out the I contained air, the pump must do a great deal 15 more work at the start, or in the pumping up period, than later, when the required vacuum, which may be as high as 29 inches of mercury, has once been set up and requires only to be maintained or continued. In some cases more than 20 four times as much power is necessary at the beginning or the operation than is needed when the vacuum has once been obtained. The cause, naturally, is the fact thatat the outset the suction pressure is higher and a greater mass of air 25 has to be removed from the condenser or other vessel that is being evacuated.

In the preferred form of my invention the pump is of the rotary vane type, and the end is gained preferably by regulating the intake of the pump. This isdone by means of a bleeder connection to the main casing of the pump adjacent the outlet thereof, but which does not communicate with the outlet and a device controlled by said connection and so arranged that the quan- 35 tity of air taken in by the pump through the inlet depends on the absolute pressure in the pump as the work of evacuation proceeds. Thus the power to actuate the pump when the operation commences is greatly reduced.

40 The nature and advantages of the invention are fully set forth in the description and drawing and the novel characteristics are defined in the claims appended hereto, but I of course reserve the right to make changes, not shown herein, but

45 of such a character as to be in accordance with the spirit and scope of the invention.

On the drawing the figure shows partly in section a construction according to my invention.

The numeral l indicates the cylinder or casing and a substantially constant open outlet 8, leading to a discharge pipe 9. The pump preferably discharges through the pipe 9 into the atmosphere or some other medium at constant pressure.

The working space [0 on the inside of the pump between the rotor and the casing is crescentshaped, so that the medium entering the pump first expands as it is admitted through the inlet 1 and is then compressed as it is expelled through the outlet 8.

This type of pump for vacuum service usually has the disadvantage that the openingpf the cylinder l to the outlet is timed by the passage of the vanes 3 over the outlet 8. When this outlet port- 8 is located with a view to giving the best performance for creating a high vacuum in the condenser, which of course will be connected to the inlet 1, the pump will at first compress to a pressure much above atmospheric, say 30 to 60 pounds per square inch gauge, with low vacuum or nearly atmospheric pressure at the suction or inlet port I. As the exhaustion of the condenser proceeds the compression pressure will drop of course, but the ratio between the suction pressure and discharge pressure tends to be constant regardless of the vacuum. Hence an excessively higher horsepower is required when the pump begins its work to reduce atmospheric pressure in the space that is being exhausted and bring it down to the point required. After the vacuum is established, of course much less horsepower is necessary. For example, in one case 'about 8 horsepower was found enough to maintaina vacuum of 29 inches, but to establish this vacuum, a peak of about horsepower was reached during 35 the initial pumping period.

My invention eliminates this peak and enables the vacuum to be obtained by the expenditure of a reasonably uniform amount of power in the entire operation from the start until the vacuum 40 is fully created. To accomplish this, I provide the cylinder l with a port ll just in advance of the outlet opening 8, and from this port extends a conduit I! to a chamber l3, in which is a diaphragm It. To this diaphragm is connected a rod [5. Movement of the diaphragm and rod is opposed by a spring IS in a part of the chamber IS. The rod I5 is connected by suitable means, such as a lever l1 and a link l8 to the arm I9 of rotary valve 20. This valve is in the intake or suction conduit 2| connecting the condenser to the inlet 1. The parts are so arranged that the spring I6 tends to open the valveand pressure on the diaphragm tends to close it. At the point where the port II is located, substantially the highest compression pressures are produced when the pump is started and the conis being pumped out, and as the maximum pressure in the casing or cylinder I drops. In other words, the quantity of air drawn into the pump is so restricted and regulated that the highest pressure in the casing I can never exceed the figure selected and the valve 20 remain open. Therefore, the pump does .not impel so great a mass of air through the outlet 8 at the start and the condenser is exhausted virtually as quickly as it would be otherwise, but very little increase in power over the amount required for normal operation-is taken by the pump when the operation of exhausting the condenser commences. The work to be done by the pump is thus more advantageously performed and the heavy initial load is obviated.

Since the pressure in the discharge pipe 9 is generallythe same as atmospheric, the pipe I2 must communicate with the interior of the pump at some point other than the outlet 8. For that reason the pipe I2 is connected to the port II so that the pressure upon the diaphragm I A varies according to an intermediate pressure within the pump. Port I I is in advance of the outlet 8 and cannot communicate with the outlet because of the spaced relationship of the vanes 3. If this pipe I2 were connected to the discharge pipe 9 and if the outlet pressure were constant, the diaphragm I4 would always remain in one position and the valve 20 would never be opened to a greater extent as the operation proceeds.

The purpose of the invention is thus obtained without waste of power and without any complicated structure being added to the pump and its connections. The regulating device comprising the valve and the chamber with the conduit I2 is quite certain in operation and inexpensive to construct and very easy to mount in operative position.

If desired, the conduit leading to the inlet I may have a valved by-pass 22 around the valve 20. This by-pass may be opened and closed by a valve 23 having an outside operating knob on the stem thereof. A compressor of this general design is inherently a constant compression ratio machine, and at the start when pressure in the pipe I9 is at least equal to the atmosphere, the compression pressure of the pump discharging through the outlet 8 is comparatively high. But as the exhaustion of the space where the vacuum is to be created proceeds, the compression pressure at both the port II and the outlet port 8 likewise will not be so great. Therefore the valve 20 is now more and more fully opened and the volume passing the valve 20 increases. Consequently the pressure at the port II, although it also drops somewhat to let the valve 20 be opened more by the spring I6, also does not fall so much, and practically no pulsations or fluctuations in the power to drive the pump occur. This mode of operation begins as soon as the pump starts and the heavy consumption of power heretofore necessary when the work of creating the vacuum commences is eliminated. After the vacuum is produced, power is of course still required to maintain it. This power is not much less than at first, and the power expenditure is virtually constant, for the initial expenditure is not much greater than what is necessary to keep the vacuum at the desired figure. 5 In other words, the discharge pressure at the outlet 8 does not go above eight pounds by the gauge and from this point it falls as the work of the evacuation proceeds and the valve 20 opens further. The distance between the port 8 and the passage II is of course slightly greater than that between any two vanes, which are preferably located at equi-distant points around the rotor 2. Hence the port 8 and passage II- never communicate with each other, because just before one of the vanes passes the outlet 8, the motion of the rotor being anticlockwise, the next vane behind passes the port II and the compressed air in the movable compression chamber or portion oi. the space I0 between said two 2 vanes will immediately discharge through the outlet 8, while the diaphragm ll will be subjected to the pressure of the next compression chamber. Some fluctuation of pressure in the diaphragm casing I3 may occur, because the 25 pressure in the next compression chamber increases as that chamber passes the port or passage II, but this fluctuation is so slight that it does not impair the desired mode of operation or prevent the desired result.

I claim:

1. A vacuum pump having inlet and outlet openings and an intermediate port between the openings and incommunicable with the outlet opening, a conduit leading from a source of fluid medium to the inlet opening, means in the conduit between said source and inlet for controlling the pump intake pressure, and a device for operating said means in response to the pressure of the fluid medium at said intermediate port.

2. A vacuum pump having inlet and outlet openings, a conduit leading from a source of fluid to the inlet opening, a pressure-responsive device controlled by a pump pressure intermediate the inlet and outlet pump pressures, said intermediate pressure being uninfluenced by the pump outlet pressure, and means operatively connected to said device for eifecting a desired restriction to the flow of fluid through said conduit and for decreasing said restriction as said intermediate pressure decreases.

3. A vacuum pump having inlet and outlet openings and an intermediate port between said openings but not communicable with the outlet opening, a conduit leading from a source of fluid to the inlet opening, a valve in the conduit for controlling the pressure of the fluid at the pump inlet, a duct connected to said intermediate port, and pressure-responsive means operatively connected to the valve and acting to move the valve to open position only at pressures lower than a predetermined pressure of the fluid in said duct.

4. A vacuum pump comprising a casing having an inlet and outlet opening and an intermediate 65 port, a rotor within the casing, said rotor having a plurality of impellers spaced around its periphery, the spaced relationship of said impellers rendering the port incommunicable with the pump outlet opening, a conduit leading from a 70 source of fluid to the inlet opening, a valve in the conduit to control the pump inlet pressure, a device to operate the valve, and a duct connecting the intermediate port and the device whereby saiddevice is actuated by pressure fluid at said port to operate said valve in accordance with variations in the pump inlet pressure.

5. A vacuum pump having an inlet and outlet opening and an intermediate port incommunicable with the outlet opening, a. conduit leading from a source of fluid to the inlet opening, a valve in the conduit to control the admission oi. fluid to the inlet opening. a spring acting to open the valve, a chamber having a diaphragm opposing the force of the spring, linkage connecting the diaphragm with the valve, and a duct connecting the intermediate port and the chamber, whereby the diaphragm is actuated by pressure fluid at said port to operate said valve in accordance with variations in the pump inlet pressure.

GEORGE H. WOODARD.

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