US2275303A - Automatic unloader for compressors - Google Patents

Description

March 3, 1942. B, Wl MANTLE 2,275,303

AUTOMATIC UNLOADER FOR COMPRESSORS Filed March 2o, 1940 ATTORNEYS P'aiented Mar. 3, 1942 UNITED 'STATES PATENT IOFFICE AUTOMATIC, UNLOADER Fon coMPREssoRs uBurr Ward Mantle, Pittsford, N. Y., assignor to The American Brake Shoe & Foundry Company, a corporation of Delaware Application Marc-'h zo, 1940, serial No. 324,902

(Cl. 23o-31) numeral I1 is mounted on a base I8 and carries 5 Claims.

This invention relates to improvements in automatic unloaders for compressors, and has for an object the provision of a settable pressure controlled unloading device which will automatically unload the compressor when the discharge pressure rises to a predeterminedvalue and will reload the compressor when this value is reduced to a second predetermined lower value. The device includes a movable member which is adapted to unseat the inlet valve or valves of the compressor and thereby unloadv the compressor.

A further object of the invention is the provision of a settable pressure controlled unloading device including plunger means and a member connected to saidplunger means and adapted to engage and unseat the inlet Valve of a compressor. The deviceA is rmounted on the compressor and said means is positioned in line with the inlet valve. Further, the device may. be adjusted so that the plunger may only effecta predeterminedmovement of the valve in unseating it.

Still another object of the invention is the provision of an unloading` device of the character described, having a tapped connection tothe cylinder of the plunger, whereby the pressure Yto which the plunger is subjected, when the unloader functions may bealso applied4 to a piston device associatedwith the other in let valve, in casesk where a two cylinder compressor, is employed. lIhe piston device consists of ya valve unseater connected to a piston.v The piston operates in a cylinder which receivespressure from the unloader device each time the latter controls. A typical example of a piston device is shown and described in Figures 4 and 5 of my co-pending application Serial Number 297,215, filed September 30, `1939. v y

Referring to the drawing:

Figure 1 is an elevation of anI air system including a tank, a motor, and a compressor equipped with my new and improved automatic unloader; v

Figure 2 is a cross-sectional elevation of the device and a portion of the cylinder of the compressor on which the unloader is mounted, and also showing an arrangement for controlling the second inlet valve in case a two cylinder compressor is employed; and

Figure 3 is a sectional view taken along the line 3-3 of Figure 2.

Referring to Figure 1, the air compressor outt includesan air storage tank II) having a discharge pipe II from the compressor connected thereto, a feed pipe I2 for leading the air to the point or points of use. The tank I also has a blow-oli valve I3 connected to the bottom of the tank through a nipple I4, a pressure gage I5 and a safety valve I6.

The compressor, generally designated by the a ilywheel I9 which is driven by a motor 20, also mounted on the base through the medium of a belt 2I. The discharge port of the compressor is connected to the pipe II and the inlet port is provided with a suitable strainer or air filter 22.

The cylinder head 23 has mounted thereon an includes a body portion '21.

automatic unloader generally designated by the numeral 25 and details of which will be described in connection with Figures 2 and 3. A pipe 24 is connected between the unloader 25 and the tank I0 and includes a valve 2 3 for shutting oli air pressure between the tank and the unloader.

The unloader, generally designated by the numeral25 and shown in detail in Figures 2 and 3, A chamber 28 is formed in the body.` A threaded holeZS cornmunicates with the chamber 28 and is tted with a threaded bushing 30 carrying a strainer formed of perforated disks 3| and 32 with suitable permeable material 33 therebetween. A pipe such as the pipe 24 is connected to the bushing 30 for leading air under pressure into the body of the valve. The valve body 21y has an extension comprised Yof a disk-like portion 34 and a threaded Shank 35. A chamber 36 is formed in the portion 34 and has a slanting passage 31 leading therefrom and lcommunicating with the vertical passage 38. 'I'he `vertical passage 38 communicates with a vertical passage 39 inthe valve body which in turn communicates with the chamber 28. The body' 21 also.has a chamber Mlformed therein and a piston 4I forms a working t in the chamber 4I] and is provided with one or more vvertical grooves 42, vthe purpose of which will presently be described.

The piston 4I is normally seated on the surface 43 about the chamber. 36. A rod 44 having threads 45 formed in its upper portion carries on its lower end an engaging member 46. 'Ihe engagingmember is provided with a hemispherical end which engages a hemispherical depression in the head of the piston 4I, thereby providing a minimum frictional engagement of the piston by the member 46, and minimizing any tendency of the piston to cock sidewise. A threaded hole 41 extends downwardly into the body .21 and communicates with the piston chamber 40. A threadedbushing 48 is threaded into'r the hole 41 and forms a bearing for the rod 44. The bushing 48 has a counterbored portion 49 whichterminates in the surface 50. `A spring Y 5I is positioned on the rod 44 between the engaging end 46 and the surface 50 and the tension of this spring is varied by screwing the bushing 48 in or out, until a desired setting is obtained, after which the'bushing may be Xed by means of the lock nut 52.

The body 21 has a smaller chamber 53 formed therein and communicating with the upper portion of the chamber 40. The skirt of the piston 4| is undercut as shown at 4|a so that when the piston is all the way up in the chamber 4i), an annular space dened by the cutaway portion Ha is in communication with the chamber 53. The one or more vertical grooves formed in the piston would at that time communicate with the annular portion (as these vertical grooves -ru out into the undercut portion Ma).

A vertical passage 54 formed inthe body'i also communicates with the chamber 53, and an angular passage 55 communicates with the passage 54 and with the upper portionof-a chamber 56 formed in the threaded shank 35.

B2 is threaded into the lbottom portion ofthe cylinder S and a hole therein forms'a guide bearing for the rod 6|. A spring 53 has one end bearing against the bushing 62 and the .other against the piston 59 and tends to urge the piston and the ,rod-5| upwardly. A bushing 64 in the cylinder 55 is provided for limiting the downward travel of the .piston 59. The lupper endof the bushing 54 is counterbored at 65. The counterboreforms .a stop for the piston 59 and is of such depth that when the piston engages `the 4bottom of the counterbore 65, the packing 6l) contacts and formsa seal with the upper end of the bushing 54 .and-prevents air from escaping around .the rod 6| when the piston has rbeen moved downwardly.

The lower end of the rod 6| has secured theretoa yoke 66 which is provided for engaging an inlet valve such as the valve 61 and forcing it off of its seat 68 against lthe urge of the inlet valve spring 69. I

In mounting the unloader on the head of a cylinder in the manner shown in Figure 1, a threaded hole is provided vin the cylinder head in line with the inlet valve and threaded to match thethreads formed on the exterior surface of. shank 35. The unloader is screwed down until the proper clearance is provided between the inlet valve |51 and the yoke 66. When .the piston is in its vnormal position, having obtained this adjustment, the lock nut 1|l is screwed down against the cylinder head Yand the unloader is thereby locked in position thereon to retain the proper adjustment.

A threaded hole in the body 21 communicates with the chamber 53 andmay be provided with a closure plug 1|.

Operation Assuming that the pressure to be maintained on the tank is from between 80 and 90 pounds, and assuming that the tension of the spring 5| is such that when 90 pounds is reached in the tank the piston 4| .will raise, it will be noted that the area of the piston subjected to the tank pressure is substantially less than the entire area of the head of the piston. However, as soon as suflicient pressure has been applied to this small area (90 pounds tank pressure as assumed above) the piston raises and since the 90 pounds per square inch is applied to more square inches of area '(the area of the piston which was previously covering up or in contact with the surface |13) the air pressure forces .the piston up until the with the upperend of bushing E4. `which is securedto the piston 59 is by this ac- 2,275,eo3 l i the chamber 40 and thence to the chamber 53 and via the passages 54 and 55.

Air pressure acts against the piston 59 and moves the same vdownwardly. until it is brought to rest within the oounterbore and the packing 6B eects a seal The rod 6| tion moved downwardly the same distance the piston-moves, and the yoke 66 on the lower end thereof engages the :inlet valve 61 and holds it off of vits seat, .thereby .preventing the compressor from pumping air.

l As soon as the air pressure on the head of the piston l||`has reduced to a point where the spring 5| urges .the piston back down on its seat 43 (above it lhas been assumed that this pressure is S0 pounds per square inch) the pressure on the head .of the piston 59 vis cut on? and leaks down by passing out around the bearing in the bushing 48 for the rodf44, AThe spring 63 urges the piston59 to the top of the cylinder 56 and thereby raises the yoke 66 oiofthe inlet valve 61, allowing it to. again .be seated so that the compressor can. operate `to .pump air,

By removing theplug 1| the devices external to the unloader may be controlled by pressure in unison with the operation of the unloader. One example of such use is shown in dot-dash lines .which illustrate .an auxiliary vpiston type unloader 12 connected to the chamber 53 by means of a pipe 13 and an elbow 1li. The auxiliary unloader 12 `has la threaded portion 15l which is screwed vinto the `cylinder head in the same manner as the portion.35 -was for the unloader and the suitable adjustment is retained by meansof the lock nut 16.

This auxiliary Aunloader is for controlling Vthe second inlet valve of a two cylinder compressor, the second inlet valve being designated by the numeral 11 andthe yoke 65a is carried on a rod la connected to the piston 'in thedevice. In such an arrangement, the tank pressure leaves the piston 4| in the manner `previously described and permits pressure to pass into .the chamber 53. This pressureis imparted to the piston 59 via the passages 54 and 55 as described above and is imparted to a similar piston in the auxiliary unloader 12 via the elbow 14 in the pipe 13, causing the inlet valve |51 and the-inlet valve 11 to be lifted oi of their seats so thatneither cylinder of the compressor can pump air.

The auxiliary piston type unloader such as 12 herein, is described and shown in detail in Figure 5 of copending application Serial Number 297,215, iled September 3Q, 1939. i

A clearance groove 8D may be formed in the threaded hole 41, and an angularhole 8| leading in from the outside air .communicates with the groove 8B. A tapped holeangular with respect t0 the hole '5| is provided with a screw 52 bymeans of which the hole A8| maybe restricted to permitthe airwithin the threaded hole l1 and inthe counterbore'dllinbushing 38,*to escape within a deiinite time limit.` This arrangement may be called a bleeder, and permits the device to operate with a snappyaction.

A further arrangementfcontemplates the omis-- sion of the passage 55, the cylinder 5G, the plston 59, its packing ,65, .the spring 63, the piston rod 6I and the engaging yoke 66. By omitting these parts the bossed portion 34 only contains the chamber 36 and the passages 31 and 38, the latter of which communicates wtih the passage 39 and when the air pressure to which 24 is connected reaches a predetermined high pressure, the piston lll raises and permits air to pass into the chamber 53 and thence out via pipe 'F3 to an auxiliary unloader 12. This permits the mounting of the device at some point remote from the cylinder head, with the result that less heat is conducted to the device and the oil in the same which passes through with the air is not carbonized.

With this modied arrangement, as many auxiliary unloaders as there are cylinders in the compressor can be connected to and controlled by the device. For example the fitting 'i4 can be' a T shaped iitting in cases where a two cylinder compressor is employed and one unloader l2 associated with one inlet valve may be connected to one side of the T and the second auxiliary unloader 72 may be associated with the second inlet valve, and may be connected to the other side of the T, in which event the device will control the two auxiliary valves in unison by air passing into the chamber 53 and via the T and connecting pipes to the auxiliary unloaders.

Compared to diaphragm types of devices, it is believed that the device herein shown and described is simpler in construction, cheaper to manufacture, and will operate with less Wear and tear on the mechanism controlled thereby.

It must be understood that it is not necessary that the auxiliary unloaders be controlled by ar master or automatic valve being operated by air delivered by the same compressor. In other words, a master valve subjected to air pressure from one source may control auxiliary unloaders on other compressors feeding air to another source.

Although a simple embodiment of the invention is herein shown and described by way of example, it is obvious that many changes may be made in the arrangement shown without departing'from the spirit of the invention as set forth in the annexed claims.

What is claimed is:

l. In combination with a compressor having an inlet valve, a discharge valve and means connected to said compressor to receive the discharge therefrom, an unloading device including a body mounted on the head of said compressor in alignment with said inlet Valve, an engaging member reciprocably carried by said body and normally positioned adjacent to said inlet valve, said member being adapted to unseat said inlet valve and said body being adjustable on said head whereby any desired clearance between saidl engaging member and said inlet valve may be obtained, a cavity in said body, a cylinder bore in said body communicating with said cavity, a piston in said cylinder, means for impressing the pressure of said discharge upon said cavity, adjustable spring means urging said piston to the end of said cylinder communicating with said cavity, pressure responsive means in said body connected to said engaging member, and a passage in said body having one end communicating with said pressure responsive means and its other end terminating in said cylinder, whereby when a predetermined pressure, in accordance with the adjustment of said spring means, is impressed upon the head said piston causing said piston to move and impart said pressure upon said pressure responsive means, the unseating of said inlet valve by said engaging member is effected.

2. In a device of the character described, a

body, a cylinder within said body, a cavity in said body, a wall between said cavity and said cylinder, an opening in said wall smaller in diameter than the diameter of said cylinder forming an annular seating face which the head of said piston normally contacts, a piston in said cylinder having its head seating on the surface of said wall and leaving exposed to said cavity an area deined by said opening and smaller than the entire area of said head, spring means urging said piston against said wall, said spring means being adjustable and being adapted to be set to apoint where a predetermined pressure against said exposed area of the piston will cause said piston to move against the urge of said spring means, means for imposing pressure on said cavity, wherebyI when said predetermined pressure is reached, said piston will move and subject the entire area of its head to said pressure, thereby making it necessary that said pressure be substantially reduced before said spring means can cause said piston to re-establish contact with said wall, a passage in said body adapted to be placed into communication with said cavity when said piston is moved by said predetermined pressure in said cavity, and means communicating with said passage and controlled by pressure from said cavity.

3. The invention according to claim 2 in which the piston in said rst cylinder has at least one groove extending longitudinally in the surface of its outer diameter from its head toward the extremity of its skirt to facilitate the passage of air from said cavity to said second cylinder the instant the head of said piston is moved out of contact with said wall.

4. In combination with a compressor having an inlet valve, a discharge valve and means connected to said compressor to receive the discharge therefrom, an auxiliary unloading device includying a body adjustably mounted on the headof said compressor in alignment with said inlet valve, an engaging member reciprocably carried by said body and normally positioned adjacent to said inlet valve, said member being adapted to unseat said inlet valve, a cylinder bore in said body, a piston in said cylinderj said body being adapted to be adjusted on the head of said compressor for obtaining any desired clearance be-` tween said engaging member and said inlet valve, an unloader member for controlling the operation of said auxiliary unloader including a body member having a chamber formed therein, means for impressing the pressure of said discharge upon said chamber, pressure responsive vvalve means within said body and subjected to said pressure, settable means holding said pressure responsive valve member on its seat against said pressure, a passage in said body placed in communication with said pressure when said piston is unseated, and meansl for leading said pressure from said passage to said auxiliary unloader.

5. A device according tol claim 2' in which said spring means is positioned Within a longitudinal cavity in said body, in which a passage leads from said longitudinal cavity to the atmosphere, and in which adjustable means is provided for constricting the opening of said last passage, thereby permitting the air to escape from said longitudinal cavity at a desired rate.

BURR W. MANTLE.

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