US2804513A - Circuit breakers dashpot mechanism - Google Patents

Description

1957 J. A. OPPEL 2,804,513

CIRCUIT BREAKERS DASHPOT MECHANISM Filed Dec. 51, 1953 23 F' .l. n i...

L? a 4 r 22 LJ I u 1 REVERS/ E FLU/D A DAYS/ P07 MECH/M/ISM 9 ZONE TIME

canlrncrs CONTACTS FULLY OPEN Inventor:

by I

Q/ His A torney.

CIRCUIT BREAKERS nAsrrror MrcrrANrsM John A. Oppel, Aidan, Pa., assignor to General Electric Company, a corporation of New York Application December 31, 1953, Serial No. 401,539

16 Claims. (Cl. Mid-34) This invention relates to a dashpot mechanism and, more particularly, to a double-acting dashpot mechanism for governing the forward and reverse travel between rest positions of a movable member, such as, the movable contact of a circuit breaker.

In order to illustrate my invention, I will describe apparatus particularly adapted for carrying it into effect in an electric circuit breaker of a particular type. It is to be understood, however, that certain features of the invention are not limited to this particular application but are of general application wherever it is desired to control the movement of a relatively movable body between spaced apart positions of rest.

In the usual fluid blast type of circuit breaker, the circuit breaker contacts are initially separated to draw an arc, and as the contact separation continues, the arc is subjected to an arc-extinguishing fluid blast action, after which further separation of the contacts provides sufficient isolation between the contacts to prevent restriking of the arc. To produce optimum interrupting characteristics in such a circuit breaker, it is desirable that the movable contact be subjected to rapid initial acceleration for separating the contacts and establishing the arc. As this separation continues and the movable contact enters the arcing zone, the moving contact should be retarded so that the arc may be subjected to effective blasting action whereby to extinguish the are. As this extinction occurs, rapid opening speed should be resumed and continued until the movable contact is smoothly decelerated at the end of its opening stroke.

In contrast to this opening operation, contact closing operation should be effected at a high speed without retardation in the arcing zone. Thus, it is desirable that the movable contact be rapidly accelerated to a relatively high speed as it begins its movement toward closed position, and this high speed should be maintained through the arcing zone and until smooth deceleration is effected at the end of the closing stroke.

It is an object of my invention to provide for a circuit breaker a new and improved dashpot mechanism which effectively controls the speed of the movable contact in accordance with the above-described speed requirements.

It is a further object of my invention to provide, in a dashpot controlling a movable contact, a control means which may be operated to adjust the opening speed of the contact in the arcing zone without affecting the contact closing speed in this zone.

It is a further object of my invention to provide for a dashpot an overflow means which not only compensates for the effect of the piston rod entering the dashpot cylinder but which also provides a metering means for controlling the speed of movement of the dashpot piston.

It is a still further object of the present invention to incorporate such an overflow means into a dashpot mechanism in such a manner that the overflow means will facilitate rapid refilling of the dashpot cylinder as the piston rod leaves the cylinder.

Still another object of this invention is to incorporate 2,8M,5l3 Patented Aug. 27, 1957 such an overflow means into a contact-controlling dashpot mechanism in such a manner that the overflow means facilitates initial acceleration of the moving contact as the closing stroke begins and in such a manner that the overflow means does not interfere with effective retardation at the end portion of the contact-opening stroke.

In carrying out my invention in one form, as applied to a circuit breaker, there is provided a dashpot mechanism comprising a cylinder and a piston reciprocable therein between a closed-contact position and a fullyopen contact position. The cylinder is provided with an overflow reservoir compensating for entry of the piston rod into the cylinder, and with an orificed passageway interconnecting the overflow reservoir and the bore of the cylinder and terminating at the bore in a mouth registering with a metering groove in the bore. This mouth is disposed between the closed-contact position and the fully-open contact position of the piston but adjacent to said fully-open contact position.

The invention will be better understood by considering the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

For a better understanding of my invention reference may be had to the accompanying drawing in which Fig. 1 is a schematic view of a circuit breaker organization containing the dashpot mechanism of the present invention. Fig. 2 is a top view of the dashpot with portions being broken away to illustrate internal details of the dashpot. Fig. 3 is a pair of opening and closing curves illustrating the approximate operating characteristics of the dashpot. Fig. 4 is a schematic view of the dashpot in which the dashpot cylinder is disposed in vertical alignment with the abscissa of Fig. 3 so that vertically aligned points in these two figures indicate corresponding positions in the stroke of the piston. Fig. 5 is an enlarged detailed view of the orifice passageway leading to the overflow reservoir. Fig. 6 is an alternative form of the orifice construction of Fig. 5.

Referring now to Fig. 1, I have shown my invention as applied to a fluid blast circuit breaker comprising an larc-chute 1 in which there are mounted relatively movable contacts 2 and 3. A conduit 4 communicating with a suitable source of gas under pressure (not shown) is provided for supplying a blast of gas to the arc chute when the contacts are separated. This blast acts to extinguish the arc which is established between the contacts when they are separated. The exhaust gases from the arc chute are conducted to atmosphere through a suitable conduit 5.

Opening and closing movement of the contact 2 with respect to contact 3 is eifected by means of a reversible fluid motor 10 operatively and insulatingly connected to contact 2 by a suitable linkage 11.

Since the specific details of the arc chute, the fluid motor, and the linkage form no part of the present invention, these parts are shown in schematic form only. Preferably, these parts are constructed as disclosed in Patent 2,436,191, issued to J. W. Timmerman 0n February 17, 1948, and assigned to the assignee of the present invention.

The linkage 11 is shown as comprising a rack 12 meshing with a pinion 13, the pinion 13 being keyed to a rotatable shaft 14 to which is fixed the crank arm 15. The movable contact 2 is suitably guided for reciprocation, as by rollers 16, and has pivotally connected thereto an insulating connecting rod or switch member 17 which is pivotally joined to the crank arm at 18. It will be apparent from this description that reciprocation of the rack 12 by the fluid motor 10 will effect reciprocation of the movable contact 2, and correspondingly, the desired relative movement between contacts 2 and 3.

In order to provide accurate speed control of the fluid motor and the movable contact 2, I have provided a double-acting dashpot mechanism 2%) which comprises a liquid-filled cylinder 21, in the bore of which there 1s mounted a reciprocable piston 22 movable against the resistance of the liquid contained in the cylinder. This piston 22 is directly coupled to the fluid motor by means including a piston rod 23 which extends into the cylinder 21. When the contacts 2, 3 of the circuit breaker are closed the piston 22 occupies a position at one end of the cylinder 21, as is shown in Fig. l, and when the contacts 2, 3 are fully opened the piston 22 occupies a position at the opposite end of the cyilnder.

For a more detailed showing of the dashpot mechanism, reference is made to Fig. 2 wherein the cylinder 21 is shown as comprising a closed-end cylindrical member 24, having tightly fitted therein a cylindrical sleeve 25 having metering slots or grooves 33 and 37 form-ed in its Wall. The cylindrical sleeve 25 is retained in place Within the member 24 by means of a plug 26 externally-threaded to engage the cooperating internally-threaded outer end of the cylindrical member 24. In order to prevent leakage of the liquid from within the dashpot, there are provided a pair of packing rings 27 and 28, packing ring 27 being compressively retained between plug 26 and a shoulder formed on cylindrical member 24, whereas packing ring 23 fits slidingly but sealing about the piston rod 23.

To aid in controlling the flow of fluid between opposite sides of the piston 22 as it is reciprocated in the cylinder 21, in a manner to be described in greater detail hereinafter, a series of bypass ducts communicating with spaced points in the bore of the cylinder are provided. More particularly, near the left hand end of the cylinder 21, as seen in Fig. 2, there is provided a duct 32 containing a check valve 31 permitting fluid flow only to the left. Disposed to the right of duct 32 (Fig. 2) is another bypass duct 33 communicating with spaced points in the bore of cylinder 21 and containing an adjustable needle valve 34, the setting of which may be varied to vary the fluid flow through bypass duct 33. In parallel fluid flow relationship with duct 33 is another bypass 36, which contains a check valve 35 permitting flow through the bypass 36 only to the right, as will be explained in greater detail hereinafter.

By referring to the schematic view of Fig. 4 together with the associated graphical representation of Fig. 3, wherein vertically aligned points represent corresponding positions in the stroke of the piston 22, the operation of the above dashpot will now be described. As the contacts of the breaker are parted by the fluid motor 10, the piston 22 moves from the closed position at A (Figs. 3 and 4) to an intermediate position at B. During this movement from A to B it is highly desirable that the movable contact 2 be rapidly accelerated. To allow for this rapid initial acceleration the dashpot should ofler relatively little resistance to the piston 22 as it moves from A to B. To this end, liquid flows comparatively freely around the piston 22 both through slot 30 as Well as through the then-opened check valve 31 in the bypass duct 32, which extends from A to B. These two passages provide relatively little fluid resistance to fluid flowing around the piston 22, hence there is little restriction to piston motion from A to B, and accordingly the fluid motor 10 may eifect rapid initial acceleration of the contact 2, as desired.

As the piston 22 continues in its movement and moves from B to C, the contact 2 moves through the arcing zone. Through this zone it is desirable to retard the piston movement and, correspondingly, the contact movement, so that effective blast action within the are chute can take place. To this end, I have impeded the flow of fluid about the piston 22 by providing no bypass groove in the portion of the cylinder wall disposed between B and C. Thus, fluid flow may take place only through the restricted bypass 33 extending from B to C and containing the adjustable needle valve 34. Check valve 35 prevents fluid flow through the bypass duct 36 during piston movement from B to C, whereas the needle valve 34 permits a restricted amount of flow around the piston through duct 33. By varying the setting of the needle valve 34, the degree of retardation which takes place as the contact moves through the arcing zone can be effectively varied. This adjustment may be set in accordance with the frequency of the electrical circuit to which the circuit breaker is to be applied; e. g. more retardation through the arcing zone is desirable in the case of 25 cycle circuits compared to that suited to the conventional 60 cycle circuit.

As the piston continues in its movement and moves from C to D, the contact 2 moves out of the arcing zone and, accordingly, it is desirable to resume high speed opening so as to effect rapid isolation of the contact 2 from contact 3. To this end, there is provided a slot 37 in the sleeve 25, which slot permits a relatively high rate of flow about the piston 22, thereby permitting rapid movement of the piston from C to D. Because this slot 37 has a portion 38 of substantially uniform cross section, a controlled and substantially constant speed from C to D is obtained.

To compensate for fluid displaced by the piston rod 23 as it enters the cylinder 24, I have provided an overflow means 40 which comprises a closed reservoir 41 communicating with the bore of the cylinder through a metering passageway 42 terminating at the cylinder bore in a mouth 43 disposed in vertical alignment with the position D. As more clearly shown in Fig. 5, the passageway 42 contains a metering orifice 44 which is so proportioned that the fluid flow through the orifice from the cylinder into the reservoir, as the piston moves from A to D, is substantially equal to the rate at which fluid is being displaced by the piston rod. This is a desirable characteristic because if the orifice were so large that the fluid flow through the orifice would be relatively unimpeded, insufficient retardation of the piston 22 would occur. Under such conditions, a comparatively large amount of fluid would flow relatively unimpeded into the reservoir while the flow to'the back side of the piston would be relatively small and a partial vacuum would be formed on the back side of the piston as it moved from A to D. Thus, it will be seen that the overflow means 40 not only compensates for the entry of the piston rod 23, but its metering orifice 44 governs the fluid flow into the reservoir in a manner effective to contribute materially to the desirable piston-retarding or dashpot effect on piston 22, particularly during passage through the arcing zone of the opening stroke.

It is desirable that the speed of the moving contact remain essentially unchanged as the piston passes from C through its position at D. However, the presence of the mouth 43 at D presents an obstacle to the attainment of this desired result because, as the forward end of the piston moves past the mouth 43, the passageway to the overflow means is no longer in parallel flow relationship with the other passage 37 which meters fluid around the piston. This parallel relationship existed up to the time the piston covered the mouth 43, as may be illustrated by the fact that as the piston moved from C to D fluid ahead of the piston would flow both through orifice 44 and around the piston through portion 38 of slot 37. Now if the mouth 43 were disposed so as to enter the bore at an ungrooved portion of the cylinder, it would follow that as the piston moved past mouth 43, the passage 42 would be completely shut off from communication with the fluid ahead of the piston, as a result of which, the compensating ability of the overflow means would be defeated at this point so that excessive retardation would occur. T o overcome this difficulty the mouth 43 is disposed directly in alignment with the groove 37 so that the passage 42 always remains in communication with the fluid being displaced through the groove by the piston moving in the cylinder. However, merely aligning the mouth 43 and the groove 37 does not restore the parallel fluid flow relationship which existed from C to D, because as the forward surface of the piston moves past the mouth 43, any volume of fluid which flows through the orifice 44 must also flow through the slot 37. This condition presents a series fluid flow relationship of the slot 37 and the orifice 44. To compensate for this transition from a parallel to a series relationship, I have modified the cross-section of the slot 37 so that its cross sectional area for a substantial portion 45 of the groove ahead of the mouth 43 is equal to the sum of the cross sectional area of slot portion 38 and the cross-sectional area of orifice 44. Thus, the slotted portion 45 admits the same flow which, from C to D, passed through slotted portion 38 and the orifice 44. This flow remaining essentially constant, the piston 22 moves through its position at D without appreciable change of speed, as is desired. It will be apparent from this description that the reduced grooved portion 38 controls the flow of fluid to the back side of the piston until the back surface of the piston moves past grooved portion 38. Thus, referring to Fig. 4, the enlargement of groove 37 from portion 38 into portion 45 may begin at any point between the mouth 43 and a point spaced from the mouth to the left by a distance equal to the effective thickness of the piston.

As the piston nears the end of the cylinder at B, it is desirable to smoothly decelerate the piston and the associated contact. To this end, the slot 37 is tapered toward the end of the cylinder so as to admita constantly diminishing flow of fluid past piston 22.

The above described opening operation is illustrated in Fig. 3 by the curve X from which it will be observed that from A to B the piston is rapidly accelerated, but

as the piston enters the arcing zone extending from B to C the piston is retarded, as desired, as indicated by the relatively steep slope of curve X between B and C. When the piston leaves this arcing zone, rapid opening speed is resumed and continued through D until smooth deceleration occurs at the end of the opening stroke at E.

In contrast to this variable speed opening operation, contact closing should be effected at high speed without retardation in the arcing zone. Thus, it is desirable that the piston be rapidly accelerated to a relatively high speed as it begins its movement toward closed position, and this high speed should be maintained through the arcing zone and until smooth deceleration is effected at the end of the closing stroke.

To produce this desired rapid initial acceleration as closing operation is initiated and the piston moves from E to D, fluid ahead of the piston 22 is permitted to flow in any of three different paths, i. e., through slot 37, through the check valve 46 in the piston 22, and into the overflow means 40. Thus it will be seen that disposing the mouth of the overflow at a point spaced from the pistons fully open contact position at E provides an additional fluid flow path which desirably permits faster acceleration as soon as a closing operation is initiated.

As the closing operation continues and the piston moves from D to C, fluid readily transfers to the back of the piston through check valve 46 and slotted portion 38, thus permitting closing to continue at high speed, as desired. As closing continues and the piston moves from C to B, i. e., the grooveless portion of the cylinder, fluid flows comparatively freely through the then open check valve 35 in duct 36 thus effectively shunting the restricted needle valve 34. This shunting of the needle valve permits the piston to sustain its velocity as the contact 2 moves through the arcing zone to close the circuit, as is desired. Preferably, the restricted passage through valve 35 is of substantially the ,same cross-section as slotted portion 38, so that no substantial change of speed occurs as the piston moves through the arcing zone toward closed position.

The desired smooth retardation at the end of the closing stroke is eflected by the taper formed in groove 30. The duct 32 which was used to permit initial opening acceleration is effectively prevented from interfering with retardation at the end of this closing stroke by means of the now closed check valve 31. This check valve 31 introduces retardation between A and B during closing which was not present during opening. I

The above-described closing operation is illustrated in Fig. 3 by the curve Y which shows that the piston is rapidly accelerated to a relatively high speed as closing operation begins, and this high speed is maintained throughout most of the stroke, as indicated by the substantially constant slope of most of curve Y. Finally, smooth de celeration occurs at the end of the closing stroke.

It should be noted that as the piston 22 moves past the mouth 43 and toward its closed position at A, fluid is flowing from the reservoir to the cylinder through the orifice 44 to maintain the cylinder 24 in liquid-filled condition and thereby to compensate for the effect of the piston rod 23 leaving the cylinder.

It will become apparent as the description proceeds that the location of the mouth 43 of the overflow passageway at a point in the cylinder bore disposed intermediate the closed and fully open contact positions but adjacent to and spaced from the fully open contact position at E is an important feature of the dashpot mechanism of this invention. This may be illustrated by a description of the characteristics of the dashpot under trip-free closing operation of the breaker contact 2. For example, assume that when contact 2 is moved from open toward closed position, a fault is present on the line and, as a result, it is necessary for the piston 22 to rapidly reverse its direction of movement as it nears the end of its closing stroke. When this rapid reversal occurs, if the cylinder is not filled with liquid on the forward side of the reversed piston, the reversely moving piston will be oifered little resistance until the cylinder space ahead of it becomes refilled with liquid. Under such conditions the reversely moving piston would accelerate rapidly until the instant it had diminished the cylinder space ahead of it sufficiently to produce a fluid-filled condition. At such an instant, the piston would be abruptly decelerated, thereby producing highly undesirable shock conditions in the breaker mechanism. To avoid these undesirable shock conditions, rapid refilling of the dashpot cylinder behind the piston should be effected as the piston moves toward closed position. I have achieved this desired result, in part, by locating the mouth 43 of the overflow passageway near the fully open contact position of the piston. Since this month 43 is located on the low pressure side of the piston throughout the greater part of the closing stroke, fluid from overflow reservoir may pass directly into the space on the low pressure side behind the piston during the greater portion of this closing stroke. Thus, favorable conditions for rapid refilling are provided as a result of the location of mouth 43. Still another factor which contributes to rapid refilling during the closing stroke is the fact that the reservoir 41 is a closed chamber so that air entrapped therein provides the system with what amounts to an air cushion. Thus, since the air entrapped above the fluid is pressurized during the opening stroke, it expands during closing to provide an appreciable positive pressure forcing the fluid from the overflow back into the cylinder, thereby facilitating rapid refilling of the cylinder during closing operation.

Another important consideration in locating the mouth 43 of the passageway 42 is that the overflow means should not interfere with deceleration of the piston at the end of the contact opening stroke. To this end, the mouth 43 is located at a point spaced from the pistons fully open contact position at E, so that the tapered portion of groove 37 can provide sufiicient deceleration of the piston at the 7 end portion of the opening stroke. Another advantage of this location of the mouth 43 is that, with the mouth so located, the overflow means actually aids in effecting the desired rapid initial acceleration of the piston as the closing stroke is begun. This is so because the passageway 42 provides an additional path through which fluid ahead of the piston may flow as the closing stroke is initiated.

Thus, it will be seen that the overflow means of the present invention is so constructed and so located that it effectively contributes to the desired rapid refilling of the cylinder and to allowing for rapid acceleration of the piston as the closing stroke is initiated. Additionally, the overflow means accomplishes these results without interfering with the desired retardation at the end of opening stroke.

To further insure that the dashpot cylinder will be filled as the piston is moved toward closed position, I have provided an alternative form of orifice which may be used instead of the orifice 44 of Figure 5. This alternative orifice construction is disclosed in Fig. 6 wherein an orifice 50 is shown as being formed in a check valve 51 which is lightlyspring biased toward closed position. Orifice 50 will function in the same metering manner as orifice 44 so long as fluid flow is into the overflow reservoir, but when fluid flow is in the opposite direction, the check valve 51 is displaced from its seat thereby permitting a large flow from the reservoir into the cylinder, thus facilitating the desired rapid refilling of the cylinder as the piston moves toward contact-closed position.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a circuit breaker having a contact movable between a closed position and a fully open position and a switch member for moving said contact, a dashpot mechanism for controlling the speed of movement of said contact comprising a liquid-filled cylinder having a reciprocable piston therein, a piston rod coupling said switch member to said piston for movement of said piston between spaced apart closed and fully open positions in said cylinder as said contact is moved between its closed and fully open positions respectively, a piston-rod compensating overflow reservoir, an orificed metering passageway connecting said reservoir with :a point in said cylinder intermediate said closed and fully open piston positions and adjacent but spaced from said fully open piston position.

2. In a circuit breaker having a contact movable between a closed position and a fully open position, a dashpot mechanism for controlling the speed of movement of said contact, said dashpot mechanism comprising a cylinder having a bore and a reciprocable piston disposed therein, means including a piston rod coupling said contact to said piston in a manner whereby said piston moves between spaced-apart closed and fully open positions in said bore when said contact is moved between its closed and fully open positions respectively, said dashpot mechanism including an overflow reservoir which compensates for the effect of said piston rod entering and leaving said cylinder, an orificed metering passageway interconnecting said reservoir and said bore and entering said bore through a mouth located intermediate said closed and fully open piston positions but adjacent to and spaced from said fully open piston position.

3. In a circuit breaker having a contact movable between a closed position and a fully open position, a dashpot mechanism for controlling the speed of movement of said contact comprising a cylinder having a bore, a

reciprocable piston movable between spaced-apart closed .said. bore through a mouth located intermediate said closed and fully open piston positions but adjacent to and spaced from said fully open piston position, said overflow reservoir being completely enclosed except for the opening provided for entry of said metering passageway.

4. In a circuit breaker having a contact movable between a closed position and a fully open position, a dashpot mechanism for controlling the speed of movement of said contact, said dashpot mechanism comprising a cylinder having a bore containing a reciprocable piston, means including a piston rod coupling said contact to said piston in a manner whereby the piston moves between spacedapart closed and fully open positions in said bore when said contact is moved between closed and fully open positions respectively, said dashpot mechanism including an overflow reservoir which compensates for the effect of said piston rod entering and leaving said cylinder, said overflow reservoir communicating with the bore of said cylinder through an orificed metering passageway which enters said bore through a mouth located intermediate said closed and fully open piston position but adjacent to and spaced from said fully open piston position, said cylinder having a generally axially extending metering groove in its bore, said metering groove being disposed in registry with said mouth and extending on opposite sides of said mouth.

5. The combination of claim 4 in which said groove is enlarged at an edge of said mouth so as to permit said piston to move past said mouth without appreciable change of speed.

6. In a circuit breaker having a contact movable between a closed position and a fully open position, a dashpot mechanism for governing the speed of movement of said contact, said dashpot mechanism comprising a cylinder having a bore, a reciprocable piston movable between spaced apart closed and fully open positions in said bore when said contact is moved between closed and fully open positions respectively, said piston being actuated through a piston rod coupled to said contact, said dashpot mechanism including an overflow reservoir which compensates for the effect of said piston rod entering and leaving said cylinder, a metering passageway interconnecting said reservoir and said bore and entering said bore through a mouth located intermediate said closed and fully open positions but adjacent to and spaced from said fully open piston position, a check valve disposed in said metering passageway and having an orifice formed therein, said check valve permitting greater flow from said reservoir than into said'reservoir.

7. A dashpot mechanism comprising a cylinder containing a fluid, a piston movable within the bore of said cylinder, a piston rod extending into said cylinder and arranged to produce reciprocation of said piston against the resistance of said fluid, an overflow reservoir compensating for the displacement of fluid by said piston rod, a passageway interconnecting said reservoir and said bore and terminating at said bore in a mouth, the bore of said cylinder having a metering groove registering with said mouth and extending axially of said bore on opposite sides of said mouth, said metering groove having a first portion extending for a substantial axial distance on one side of said mouth and a second portion disposed essentially on the other side only of said mouth, said first portion of said groove having a cross-sectional area substantially greater than the cross-sectional area of said second portion in the region where said two groove portions meet.

8. The dashpot mechanism of claim 7 in which said passageway contains a metering orifice of a predetermined cross-sectional area, said first portion of said metering groove having a cross-sectional area substantially equal to the sum of the cross-sectional area of said orifice plus the cross sectional area of said second portion of said metering groove.

9. A dashpot mechanism comprising a cylinder containing a fluid, a piston movable within the bore of said cylinder, a piston rod extending into said cylinder through an end wall thereof and arranged to produce reciprocation of said piston against the resistance of said fluid, an overflow reservoir compensating for the displacement of fluid by said piston rod, a passageway interconnecting said reservoir and said bore and terminating at said bore in a mouth, the bore of said cylinder having a metering groove registering with said mouth and extending axially of said bore on opposite sides of said month, said metering groove having a first portion extending for a substantial axial distance on one side of said mouth and a second portion disposed essentially on the other side only of said mouth, said first portion of said groove having a cross-sectional area substantially greater than the cross-sectional area of said second portion in the region where said two groove portions meet, the enlarged portion of the metering groove being disposed on that side of said month which is axially opposed to the cylinder wall through which the piston rod enters said cylinder.

10. A dashpot mechanism comprising a cylinder containing a fluid, a piston movable within the bore of said cylinder, a piston rod extending into said cylinder and arranged to produce reciprocation of said piston against the resistance of said fluid, an overflow reservoir compensating for the displacement of fluid by said piston rod, a passageway interconnecting said reservoir and said bore and terminating at said bore in a mouth, the bore of said cylinder having a metering groove registering with said mouth and extending axially of said bore on opposite sides of said mouth, said metering groove having a first portion of substantially uniform cross-section extending for a substantial axial distance on one side of said mouth and a second portion of substantially uniform crosssection disposed essentially on the other side only of said mouth, said first portion of said groove having a crosssectional area substantially greater than the cross-sectional area of said second portion in the region where said two groove portions meet.

11. A dashpot mechanism comprising a cylinder containing a fluid, a piston movable within the bore of said cylinder, a piston rod extending into said cylinder and arranged to produce reciprocation of said piston against the resistance of said fluid, an overflow reservoir compensating for the displacement of fluid by said piston rod, a passageway interconnecting said reservoir and said bore and terminating at said bore in a mouth, the bore of said cylinder containing a metering groove registering with said mouth and extending axially along said bore on opposite sides of said mouth, said groove having a first portion located on one side only of said mouth and extending for a substantial axial distance from said one side of said mouth and a second portion extending on the other side of said mouth from a point axially spaced from the mouth by a distance not exceeding the effective thickness of said piston, said first portion having a substantially larger cross-sectional area than said second portion in the region where said two portions meet.

12. In a circuit breaker having a contact movable between a closed position and a fully open position and through an arcing zone disposed between said two positions, a dashpot mechanism for governing the speed of said contact, said dashpot mechanism comprising a cylinder enclosing a reciprocable piston coupled to said contact so as to occupy a first position at one end of the bore of said cylinder when said contact is in closed position and a second position at the opposite end of said bore when said contact is in fully-open position, an intermediate portion of said bore corresponding to said arcing zone, and control means for adjusting the speed of the piston as it moves through said arcing zone from said first portion to said second position, said control means comprising a pair of bypass ducts communicating with said bore at points corresponding to the limits of said arcing zone, said ducts being in parallel flow relationship and one of said ducts containing a check valve.

13. In a circuit breaker having a contact movable between a closed position and a fully-open position and through an arcing zone disposed between said two positions, a dashpot mechanism for governing the speed of said contact, said dashpot mechanism comprising a cylinder enclosing a reciprocable piston coupled to said contact so as to occupy a first position at one end of the bore of said cylinder when said contact is in closed position and a second position at the opposite end of said bore when said contact is in fully-open position, an intermediate portion of said bore corresponding to said arcing zone, and control means for adjusting the speed of the piston as it moves through said arcing zone from said first position to said second position, said control means comprising a bypass duct and a check valve arranged in said duct in such a manner that adjustment of said control means has no substantial eflect on the speed of the piston as it moves through said arcing zone from said second position to said first position.

14. In a circuit breaker having a contact movable between a closed position and a fully open position and through an arcing zone disposed between said two positions, a dashpot mechanism for governing the speed of said contact, said dashpot mechanism comprising a cylinder, a reciprocable piston movable within the bore of said cylinder and coupled to said contact so as to occupy a first position at one end of said bore when said contact is in closed position and a second position at the opposite end of said bore when said contact is in fully open position, an intermediate portion of said bore corresponding to said arcing zone, and control means for adjusting the speed of the piston as it moves through said arcing zone from said first position to said second position, said control means comprising a pair of bypass ducts arranged in parallel flow relationship and communicating with said bore at points corresponding to the limits of said arcing zone, a check valve disposed in one of said ducts and arranged to block flow through said one duct during movement of said piston through said arcing zone in a direction from said first to said second position.

15. The arrangement of claim 14 in combination with an adjustable valve which is disposed in the second of said ducts and is adjustable to control the flow of fluid through said second duct.

16. In a circuit breaker having a contact movable between a closed position and a fully open position, a dashpot mechanism for controlling the speed of movement of said contact, said dashpot mechanism comprising a cylinder having a bore and a reciprocable piston disposed therein, means including a piston rod coupling said contact to said piston in a manner whereby said piston moves between spaced apart closed and fully open positions in said bore when said contact is moved between its closed and fully-open positions respectively, said dashpot mechanism including an overflow reservoir which compensates for the efiect of said piston rod entering and leaving said cylinder, an orificed meter- 11 7 7 ing passageway interconnecting said reservoir and sai 1,724,571 bore and entering said bore through a mouth located ad- 2,040,262 jacent to said fully-open piston position. 2,298,208

References Cited in the file of this patent 5 UNITED STATES PATENTS 1,689,841 Powell Oct, 30, 1928 12 Fiddyment Aug. 13, 1929' Kruckenberg et a1 -1 May 12, 1936 Gilbert et a1. Oct. 6, 1942 FOREIGN PATENTS France July 6, 1926

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