US3143297A

US3143297A - Rotary lawn sprinkler including spray area adjusting means

Info

Publication number: US3143297A
Application number: US315522A
Authority: US
Inventors: Jepson Ivar
Original assignee: SUUBEAM CORP
Current assignee: SUUBEAM Corp
Priority date: 1963-10-11
Filing date: 1963-10-11
Publication date: 1964-08-04
Anticipated expiration: 1981-08-04

Description

Aug.- 4, 1964 JEPSON 3,143,297

ROTARY LAWN SPRINKLER INCLUDING SPRAY AREA ADJUSTING MEANS Filed 001.- 11, 1963 United States Patent 3,143,297 RQTARY LAWN SPRINKLER 1N CLUDlNG SERAY AREA ADJUSTING MEANS lvar lepson, 0a Park, Ill., assignor to Sunbeam Corporation, Chicago, 11., a corporation of Illinois Filed Get. 11, 1963, Ser. No. 315,522 11 Claims. (ill. 239-251) The present invention relates to fiuid dispersing apparatus, and more particularly, to rotary lawn sprinklers of the type utilized by individual home owners. The present invention is related to Iepson Patents 2,335,281, 2,591,073 and 2,619,381, all assigned to the same assignee as the instant application.

The twin arm rotary lawn sprinklers of the type disclosed in the above mentioned Jepson patents have enjoyed substantial commercial success and the sprinklers following the teachings of the lepson Patent 2,591,073 have been extensively sold throughout this country. The success attained by the sprinkler can be attributed in part, to its ability to uniformly disperse water over a circular area of lawn of selectable diameter. The previous sprinkler has twin spray arms which are oppositely disposed and mounted downwardly from the sprinkler head. A plurality of spray orifices are spaced in substantial alignment along each arm which are rotatably supported along their axis so that elevation of the orifices can be varied to produce various watering diameters. That is to say as the elevation of the orifices is raised the sprinkler will water in a larger diameter. It is readily understood that the maximum elevation of the orifice can not lie in the vertical plane since it is necessary that the orifices be positioned so the water egressing therefrom has a lateral component to cause rotation of the sprinkler head. It is appreciated that the oppositely disposed spray arms not only uniformly disperse water, but also cancel forces on the main sprinkler head bearings due to centrifugal force and reaction to the spray being emitted from the discharge orifices. While this sprinkler has been a great success commercially, there is a need for a sprinkler having the same desirable watering characteristics but which would be considerably easier to manufacture and having a lower overall cost. Elimination of one of the spray arms and utilization of a single spray arm would obviously reduce the sprinkler cost. The difficulty with this approach, however, is that considerable unbalanced forces would be imposed upon the bearings due to the use of a single arm. It is well understood that the forces upon the main bearings must be held to an obsolute minimum in order that the head may be rotated freely. If the rotational speed of the head is reduced, the water emitted from the discharge orifices in the arms will not be sufficiently broken up to obtain uniform distribution, and the individual spray droplets leaving the sprinkler will not have sufficient force to reach the maximum distance required.

Accordingly, it is the object of the present invention to provide an improved lawn sprinkler which is easier to manufacture and lower in cost.

Another object of the present invention is to provide a rotary lawn sprinkler having a single spray arm for uniformly dispersing water.

Still another object of the present invention is to provide a one arm rotary sprinkler having a means for counterbalancing the forces by a single arm in order to reduce the frictional load on the sprinkler head bearings.

it is another object of the present invention to provide a one arm rotary sprinkler which is constructed in such a manner as to reduce the unbalanced force on the sprinkler hearing by having means to nullify both the Patented Aug. 4., 1964 centrifugal force of the single rotary arm and the reaction force of the fluid being emitted therefrom.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention wiil be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

FIG. 1 is a side elevation view of a complete sprinkler embodying the present invention;

FIG. 2 is an enlarged sectional view of the sprinkler;

PEG. 3 is a side projectional view of the sprinkler head shown in FIG. 2 with the control knob in the raised position; and

FIG. 4 is an end projectional view of the sprinkler head in FIG. 2. I

Referring now to the drawings, there is illustrated a water dispersing device generally indicated by the reference numeral 19, which is commonly designated as a lawn sprinkler. It comprises the conventional supporting base or stand 11, which is illustrated as an integral aluminum casting. Naturally, the base may be made from many difierent materials, such as plastic, and can be integral or made from separate components. The base 11 includes a lower portion 12 and an upright portion 13. A fluid conducting passageway is molded into the base having a substantially horizontal portion 14 which communicates with a vertically extending portion 15. Disposed at the opened end of the horizontal passageway 14 is a suitable coupling 16 which is adapted to be removably connected with a garden hose as commonly found in the yard. The upper end of the vertical passageway is threaded to receive a hollow fixed bearing support 17. The bearing 17 may be made from many different materials, but according to the present embodiment of this invention, it is made of bearing bronze. Inas much as the bearing 17 is hollow, there is afforded a continuous conduit for transmitting water under pressure from the coupling 16 to the top of the bearing 17.

In accordance with the present invention, a rotatable sprinkling head 2% is provided to disperse the water transmitted upwardly through the base. The sprinkler head 20 includes a spray arm support member 21 preferably of molded plastic having a depending steel sleeve bearing 22 which is rotatably mounted on the base by the outside diameter of the sleeve bearing 22 being received within the inside diameter of the fixed bearing 17. The sleeve bearing 22, as illustrated in FIG. 2, can be molded, pressed or the like into permanent engagement with supporting member 21. In order to retain the sleeve bearing 22 against upward displacement with respect to bearing 17, a retaining ring 23 is pressed in an annular recess near the bottom of the sleeve bearing 22. In the present embodiment, a thrust bearing 24, which may be made of phenolic, is disposed between the top of retaining ring 23 and the bottom of the fixed bearing 17 to absorb the upward force exerted by the retaining ring 23 as a result of the reaction force of the water passing through the head 20.

The principal axis of rotation of the sprinkler head 29 is denoted by the reference number 18 in FIG. 2. As may be readily seen in FIG. 2, the integral supporting member 21 comprises a hollow upright portion 21a which is disposed generally along the vertical principal axis 18 and a transverse portion which is generally dis posed along a transverse axis 37 and defines a chamber 25 which is in fiuid communication through the sleeve bearing 22 into the vertical and horizontal base passage- Way which terminates at coupling 16. Thus, when a from the spray arm 30.

hydrant is connected to the sprinkler by means of a garden hose, fluid under pressure will be introduced into the base and directed upwardly into the support member chamber 25. This chamber has a generally circular cross section which is disposed along the transverse axis 37. The transverse axis is less than 90 degrees from the horizontal plane. At either end of the chamber 25 are coaxial lower and upper openings, 26 and 27 respectively.

Extending from chamber 25 through opening 26 in a downwardly angled direction is tubular spray arm 30, having the lower end closed by a cap screw 31. The

elongated arm 30, which extends longitudinally from the support member 21, is mounted for rotation about its own axis which lies along axis 37. Preferably the cap screw is received within an internally threaded portion at the end of the tubular arm 30 and is removable for the purpose of emptying sediment and foreign matter In order to locate the elongated tubular arm 30, an annular enlargement 32 is formed on the periphery thereof. A plurality of

discharge orifices

33a, 33b and 330 are spaced axially with respect to member 21 along the arm 30 in substantially linear.

alignment. The upper portion of arm 30 has transverse openings or access 34 formed therethrough and positioned within the chamber 25. The chamber is sufliciently large to provide ample clearance around the arm so that fluid may easily enter the openings 34. Therefore, the tubular arm 30 and the discharge orifices 33a, 33b and 33c are in fluid communication with the chamber 25. While different orifice diameters will function properly, it has been determined that good fluid distribution can be accomplished with diameters of .125, .125 and .063

inch for

orifices

33a, 33b and 330 respectively. With these orifice sizes the sprinkler will disperse approximately 200 gallons per hour when furnished with water at 20 psi. In order to prevent fluid leakage between the arm 30 and the chamber 25, an O-ring 35 is disposed in an internal annular recess 28 in the support member 21.

As best can be seen in FIG. 2, a manually operable control knob is mounted coaxially with arm 30 and extending upwardly through upper opening 27 in member 21. The control knob 40' is positioned within the support member 21 and is rigidly joined to the upper end of spray arm 30 by a locking pin 41 which transverses both parts. The control knob 40 defines an elongated cylindrical recess 42 which receives the open end of arm 30 so that the recess 42 is in fluid communication with the" diameter of the enlargement 32 so that the washer is trapped between the enlargement 32 and the bottom of the support member 21. The spring washer is designed to exert a longitudinal force upon arm 30 in a direction parallel to the spray arm axis 37, thus biasing the locating tooth 43 of the control knob into engagement with the mating teeth 44 of the support member. If it is desired to angularly rotate the'control knob 40 and arm 30 with respect to the support member 21, the

. knob is raised sufficiently for the tooth 43 to clear teeth 44 against the biasing force of the spring 45 and rotate it to a selective position, whereupon the spring 45 will re-engage the mating teeth providing a detent type ac- :tion.

Printed along the upper surface of control knob 48 are indicia 46 which cooperate with a triangular mark 47 centrally positioned on the top of support member 21 to visually denote the relative position of control knob 40 with the support member 21. In order to prevent leakage between member 21 and knob 4! an O-ring 49 is positioned between the inside surface defining chamber 25 and on a reduced outside diameter of the knob. As can easily be seen in FIG. 4, the knob 40 has been rotated and releasably locked in the maximum spraying diameter which, in this illustrated embodiment, is set for 50 feet with the discharge orifices raised to the highest operable elevation. When a smaller diameter is to be wetted by the sprinkler, the control knob 4t is rotated in a counterclockwise direction with respect to support member 21, as viewed in FIG. 4, so that the orifice elevation is reduced and, in this particular embodiment, would wet a diameter of approximately 5 feet. Therefore, the operator may conveniently select the diameter at which he wishes the sprinkler to water by merely rotating the control knob 49 with respect to the support member 21 which will correspondingly position the orifice nozzles for the correct elevation.

According to the present invention, the control knob 49 should be of sufiicient mass to ofiset the centrifugal force imposed upon the

bearings

17 and 22 by the rotation of arm 30 about the principal axis of rotation 18.

When water under pressure is passed through the sprinkler 10, a reactionary force is exerted upon arm 30 due to the water egressing through

orifices

33a, 33b and 330. In order to reduce the etfect of this reactionary force, a balancing hole 48 into recess 42 of knob 40 is positioned in spaced parallel relationship with the discharge orifices. Thus, the reaction of the water egressing through balancing hole 48 reduces the bending moment imposed upon the bearings due to the orifices reactionary force on arm 30.

In operation the sprinkler 10 is connected to a lawn hose by the coupling 16. When water under pressure is introduced into the sprinkler, it is channeled through the horizontal base passageway 14 and then directed upwardly through the vertical passageway 15 through the hollow sleeve bearing 22 into the support chamber 25 where it enters through openings 34 into the spray arm 30. The major portion of the water entering through openings 34 is directed downwardly through the tubular arm 30 to be discharged through one of the

orifices

33a, 33b or 330. When the water egresses through the orifices, a rotary motion is imparted to the sprinkler head which causes rotation about its principal vertical axis 18. Depending upon the angular relationship between the orifices and the supporting member 21, the water is dispersed over a selected diameter of the area to be Wetted. In addition, a small portion of the water is directed upwardly through the end of the arm 30 into the recess 42 of knob 40 to be discharged through balancing opening 48 to reduce the reactionary force exerted on the sprinkler bearings due to the Water egressing through the discharge orifices. Further, the control knob 46 has a sufficient mass to nullify the centrifugal force upon the sprinkler bearings due to the rotation of arm 30.

Whenever it is desired to change the watering radius, the control knob 40 is raised slightly against the biasing force of washer 45 to disengage the knob tooth 43 from the corresponding support member teeth 44 so that the angular relationship between the control knob and the support member may be varied in order to establish the correct elevation of discharge orifices. This operation is I facilitated by the indicia 46 on the knob which may be rotated with respect to the mark 47 on the support member. After the new setting has been obtained, the control knob 40 is released so that the spring 45 will bias the knob tooth 43 into locking engagement with support teeth 44.

In the successful operation of a rotating sprinkler it is necessary that thesprinkler head rotating torque generated by the tangential discharge of water under pressure through watering orifices be suflicient to overcome the sprinkler head bearing friction. It is, therefore, imperative that the frictional losses in the bearing be held to an absolute minimum. inherently, a one arm rotary sprinkler exerts considerable unbalanced force upon the sprinkler bearing which, if not corrected for, would prevent the sprinkler from functioning properly. The sprinkler which has been here described in detail is able to realize the material cost saving of having a single arm, but has been designed in such a manner to nullify the unbalanced forces exerted or imposed upon the sprinkler bearings.

While there has been illustrated and described a particular embodiment of the present invention, it will be understood that changes and modifications may occur to those skilled in the art, and it is, therefore, contemplated by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A spray head for use with a rotary sprinkler of the type for watering a lawn comprising a hollow support member defining a chamber therein and disposed for rotation about a principal axis, means for conveying water under pressure into said chamber, a single elongated spray arm extending from said member at an angle less than 90 from said principal axis, said arm being hollow and in fluid communication with said chamber, plurality of discharge orifices defined in said arm and spaced in substantially longitudinal alignment whereby the fluid forced through said orifices can wet a given lawn area, an adjustable control knob disposed on the opposite side of said member from said arm, said knob and arm being mounted on said support member for rotation about a spray axis defined by the longitudinal axis of said arm, and said knob and arm being connected together so that rotation of said knob causes a corresponding rotation of said arm for varying the diameter of lawn area to be wetted, and means counterbalancing the centrifugal force of said arm when the head is rotated about the principal axis.

2. In a lawn sprinkling device including in combination: a ground engaging base; a hose coupling associated with said base and adapted to be removably attached to fluid supply; said coupling connected to a substantially horizontal passageway which is in fluid communication with a vertical passageway; fixed bem'ng mounted within the upper portion of said vertical passageway and aligned to support rotation about vertical principal axis; a sprinkler head comprising a hollow support member having a depending sleeve bearing received within said fixed bearing for rotation about said principal axis and being in fluid communication with said vertical passageway; a single elongated hollow spray arm extending longitudinally in a downwardly angled direction toward said base from said member and being in fluid communication therewith; plurality of discharge spray orifices disposed on said arm in substantial longitudinal alignment for distributing the fluid over a selected area to be wetted; a control knob coaxial with said arm and positioned on the opposite side of said member from said arm, means rigidly locking said knob to said arm, said knob and arm supported for rotation about the longitudinal axis of said arm whereby rotation of said knob results in a corresponding rotation of said arm, sealing means preventing fluid leakage between said member and knob and said member and mm, indicia on said member for readily locating said knob in angular relationship with said member for selecting different diameters of wetting, and means counterbalancing the centrifugal force imposed upon said fixed bearing due to rotation of said arm about the principal axis.

3. The lawn sprinkling device or" claim 2 wherein said counterbalancing means comprises at least in part the mass of said head disposed on the side of principal axis opposite said arm.

4. A sprinkling device according to claim 3 wherein said sealing means includes an O-ring disposed between said member and knob and another O-ring between said memher and arm.

5. A rotary reaction lawn sprinkler of the type used with a garden hose comprising in combination: a base having a fluid passageway terminating at one end with a coupling adapted to removably receive the garden hose and at the other with a base bearing, a rotatable sprinkler head including a support member defining a chamber therein and having a depending bearing which cooperates with said base bearing to support said member for rotation about a principal axis defined by said bearings, said chamber being in fluid communication with said base passageway, an elongated tubular spray arm extending long tudinally in a downward direction from an opening into said chamber and supported for rotation about the longitudinal axis of said arm, said arm defining an access disposed within said chamber whereby said arm is in fluid communication with said base passageway, plurality of discharge orifices on said arm spaced in substantial alignment along the longitudinal axis, an adjustable hollow control knob coaxial with said arm and extending from said member on the opposite side of said member from said arm, means locking said knob to said arm near the end of said arm directed upwardly whereby said arm and knob are in fluid communication, and counterbalance means for canceling the forces imposed upon said bearings by the centrifugal force of said arm while rotating about said principal axis and by the reaction force of fluid egressing from said orifices.

6. The sprinkler according to claim 5 wherein said counterbalance means includes the mass of said control knob and a balancing opening defined by said knob in fluid communication with said chamber, said knob balancing opening being in parallel alignment with said arm orifices in order to reduce reaction force imparted to said bearing by the fluid egressing from said arm.

7. In combination: an upright sprinkler base; a sprinkler head rotatably mounted on said base; fluid conveying means in said base for channeling fluid into said head; said head comprising a support member defining a chamber therein; a single tubular spray arm extending from said member and in fluid communication with said chamber, a control knob associated with said arm and extending from the opposite side of said member from said arm, said knob defining a fluid channel which is open to said chamber, plurality of spaced fluid discharging orifices in substantial alignment on said arm for disbursing the fluid on a selected area to be wetted, a balancing opening defined by said knob which is aligned for emitting fluid a direction parallel to the arm orifices whereby reducing the reaction force upon said head by fluid egressing from said arm orifices and said knob being of sufiicient mass to nullify the centrifugal force imposed upon the head by said arm.

8. In a rotary lawn sprinkler of the type to be used with a garden hose for watering a selected area of the lawn including a ground engaging base having a fluid passageway with a coupling disposed at one end for removably connecting to a water pressure source and a vertically aligned fixed bearing positioned at the other end; a sprinkler head comprising a support member defining a chamber therein and having a hollow sleeve bearing depending therefrom cooperating with said base bearing for supporting said member for rotation about a principal axis defined by said bearings; a single, elongated, tubular arm extending from said member in a downwardly direction with the longitudinal portion of said arm defining the spray arm axis, said arm being closed at the end projecting from said member and open at the other, plurality of discharge orifices spaced along the longitudinal side of said arm, a control knob coaxial with said arm and extending from said member in the opposite direction from said arm, said knob defining a fluid channel which receives the open end of said arm, and said knob being rigidly fastened to said arm; an access formed in the portion of said arm received within said chamber whereby said base passageway, arm and knob channel are in fluid communication; releasable locking means between said knob and member for permitting the knob to be oriented in an angular relationship with the support member; indicia between said knob and member for selectively orienting the discharge arm orifices whereby different diameters can be wetted; O-ring seals positioned between said member and knob and said member and arm to prevent leakage; a balancing opening formed by said knob into said channel in a direction parallel to said arm orifices for reducing the reaction force caused by fluid egressing from said orifices upon said bearing; and said knob being of suflicient mass to effectively reduce the centrifugal force imposed upon said bearings due to the rotation of said head about the principal axis whereby the bearings can operate with a minimum of frictional losses.

9. In a rotary lawn sprinkler for use with a fluid source under pressure to disperse the fluid over a selected area of a lawn including: a ground engaging base having a fluid passageway with a coupling disposed at one end which is adapted for removable connection with the fluid source under pressure and a fixed sleeve bearing positioned near the other end; said fixed bearing defining a vertical prinpal axis of rotation; a hollow support member having an upright portion containing a passageway therethrough and a transverse portion which defines a cylindrical chamber disposed along a transverse axis; said upright member portion having a rotatable sleeve bearing extending therefrom which is received within said fixed bearing for cooperating therewith for rotating said member about said vertical axis; said rotatable sleeve bearing being in fluid communication with said base passageway and said upright passageway which opens into said chamber; said transverse member portion forming coaxial upper and lower openings at opposite ends of said chamber which lie on said transverse axis; an elongated, substantially tubular spray arm extending along said transverse axis from said lower opening in transverse member portion with a plurality of discharge orifices spaced along the longitudinal side of said arm in substantial alignment; said arm .being closed at the end remote from said support member and having a transverse opening formed near the other end within said chamber whereby said orifices are in fluid communication with said chamber; an annular enlargement around periphery of said arm between the ends thereof and positioned outside of said chamber adjacent said lower opening in transverse member portion in order to position said arm longitudinally with respect to said support member; an annular recess formed adjacent said lower chamber opening; an O-ring seal disposed in said recess 'for establishing a fluid seal between said chamber and arm; a control knob positioned at said upper chamber opening for rotation about said transverse axis; a second O-ring seal positioned between said knob and angled support portion for preventing fluid from egressing therefrom; said knob defining a recess therein which is disposed along said transverse axis and is adapted to receive and support upper end of said arm; means rigidly locking said knob and arm together whereby any rotation of said knob about the transverse axis would produce a corresponding rotation of said arm; said knob being of suflicient mass to reduce the centrifugal force of said arm imposed on said bearings while said support member is rotating about said principal axis due to fluid egressing from said orifices.

10. The sprinkler of claim 9 wherein said transverse axis is less than from the horizontal.

11. In a rotary lawn sprinkler for dispensing a fluid from a pressure source over a selectable area of lawn including: a base having a passageway therein with a coupling at one end adapted for releasable connection with the fluid source and a vertically disposed fixed bearing at the other end; a sprinkler head comprising an integral support member having an upright portion and transverse portion defining a transverse axis which is less than 90 from a horizonal plane; a movable sleeve bearing extending from the bottom of said upright portion which is received in said fixed bearing and is adapted for rotating said sprinkler head about the vertical bearing axis; locking means at the bottom of said movable bearing for securing said movable bearing from vertical displacement with respect to said base; said transverse portion defining a cylindrical chamber disposed along said transverse axis and coaxial upper and lower openings formed at opposite ends thereof; an elongated tubular spray arm extending through said lower opening along said transverse axis and having a plurality of spaced discharge orifices in substantial linear alignment; said arm being hollow with a closed lower end and transverse openings formed near the upper end which are within the chamber so that said orifices are in fluid communication with said coupling, said cylindrical chamber being sufiiciently large to provide ample clearance around said arm so that fluid may easily enter said transverse openings, an annular enlargement around periphery of said arm between the ends thereof and positioned outside of said chamber adjacent said lower opening in transverse member portion in order to position said arm longitudinally with respect to said support member; an annular recess formed adjacent said lower chamber opening; an O-ring seal disposed in said recess for establishing a fluid seal between said chamber and arm; a control knob positioned at said upper chamber opening for rotation about said transverse axis; a second O-ring seal positioned between said knob and angled support portion for preventing fluid from egressing therefrom; said knob defining a recess therein which is disposed along said transverse axis and is adapted to receive and support upper end of said arm; means rigidly locking said knob and arm together whereby any rotation of said knob about the transverse axis would produce a corresponding rotation of said arm; said knob being of suflicient mass to reduce the centrifugal force of said arm imposed on said bearings while said sprinkler head is rotating about said bearings due to fluid egressing from said orifices.

References Cited in the file of this patent UNITED STATES PATENTS 2,086,515 Evans July 6, 1937 2,335,332 Wright Nov. 30, 1943 2,591,073 Jepson Apr. 1, 1952 2,619,381 Jepson Nov. 25, 1952

Claims

1. A SPRAY HEAD FOR USE WITH A ROTARY SPRINKLER OF THE TYPE FOR WATERING A LAWN COMPRISING A HOLLOW SUPPORT MEMBER DEFINING A CHAMBER THEREIN AND DISPOSED FOR ROTATION ABOUT A PRINCIPAL AXIS, MEANS FOR CONVEYING WATER UNDER PRESSURE INTO SAID CHAMBER, A SINGLE ELONGATED SPRAY ARM EXTENDING FROM SAID MEMBER AT AN ANGLE LESS THAN 90* FROM SAID PRINCIPAL AXIS, SAID ARM BEING HOLLOW AND IN FLUID COMMUNICATION WITH SAID CHAMBER, PLURALITY OF DISCHARGE ORIFICES DEFINED IN SAID ARM AND SPACED IN SUBSTANTIALLY LONGITUDINAL ALIGNMENT WHEREBY THE FLUID FORCED THROUGH SAID ORIFICES CAN WET A GIVEN LAWN AREA, AN ADJUSTABLE CONTROL KNOB DISPOSED ON THE OPPOSITE SIDE OF SAID MEMBER FROM SAID ARM, SAID KNOB AND ARM BEING MOUNTED ON SAID SUPPORT MEMBER FOR ROTATION ABOUT A SPRAY AXIS DEFINED BY THE LONGITUDINAL AXIS OF SAID ARM, AND SAID KNOB AND ARM BEING CONNECTED TOGETHER SO THAT ROTATION OF SAID KNOB CAUSES A CORRESPONDING ROTATION OF SAID ARM FOR VARYING THE DIAMETER OF LAWN AREA TO BE WETTED, AND MEANS COUNTERBALANCING THE CENTRIFUGAL FORCE OF SAID ARM WHEN THE HEAD IS ROTATED ABOUT THE PRINCIPAL AXIS.