CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 61/915,838 filed on December 13, 2013, and entitled "MECHANICAL VENT VALVE," U.S. Provisional Application No. 61/915,847 filed on December 13, 2013, and entitled "MECHANICAL VENT VALVE WITH REMOTE VISUAL INDICATION OF INJECTOR RESET," U.S. Provisional Application No. 61/915,854 filed on December 13, 2013, and entitled "MECHANICAL VENT VALVE WITH FLUID RECIRCULATION CAPABILITY," U.S. Provisional Application No. 61/915,859 filed on December 13, 2013, and entitled "SELF-ADJUSTING PRESSURE RELIEF," U.S. Provisional Application No. 61/915,864 filed on December 13, 2013, and entitled "ADJUSTABLE RESTRICTED ORIFICE," and U.S. Provisional Application No. 61/915,871 filed on December 13, 2013, and entitled "SELF ADJUSTING RESTRICTED ORIFICE," the disclosures of which is incorporated by reference in its entirety.

BACKGROUND

Machinery often requires lubrication to function. Seals, pistons, and bearings require lubrication with small, measured amounts of grease or oil over short, frequent time intervals to prevent wear, corrosion, over-lubrication, or under-lubrication. Lubricant fluid is injected at specific locations that require lubrication by lubricant injectors. Lubricant fluid is drawn from a lubricant reservoir and pumped to the lubricant injectors via a lubricant work line. The lubricant injectors are configured to fire and inject a set, small amount of lubricant fluid to the specific location within the machinery once the pressure within the lubricant work line reaches a predetermined level. After the lubricant injectors have fired, the lubricant is drained from the lubricant work line, resetting the lubricant system for another lubrication cycle.

SUMMARY

In a first embodiment, an adjustable restricted orifice comprises a restriction line, a piston, a vent path, and a stop. The restriction line defines a bore, and the restriction line includes a fluid inlet and a fluid outlet. The piston is disposed within the bore. The vent path is defined as a clearance between the piston and the bore. The stop projects from the restriction line into the bore, and the stop prevents a length of engagement between the piston and the bore from decreasing due to any upstream pressure acting on the piston.

In a second embodiment, a self-adjusting restricted orifice comprises a restriction line, a piston, a vent path, and a spring. The restriction line defines a bore, and the restriction line includes a fluid inlet and a fluid outlet. The piston is at least partially disposed within the bore, and the piston has a free end and a retained end. The vent path is defined as a clearance between the piston and the bore. The spring is disposed within the bore, with a first end of the spring attached to the retained end of the piston, and a second end of the spring attached to the restriction line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a lubrication system that includes a mechanical vent valve.

FIG. 2A is a cross-sectional view of a mechanical vent valve in a first operating state according to an embodiment of the present invention.

FIG. 2B is a cross-sectional view of a mechanical vent valve in a second operating state according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a restriction according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a restriction according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a restriction according to an embodiment of the present invention.

DETAILED DESCRIPTION FIG. 1 shows a block diagram of lubrication system 10, a system that receives, stores, and supplies lubricant fluid. Lubrication system 10 includes pump 12, reservoir 14, mechanical vent valve 16, supply line 18, pump line 20, return line 22, lubrication line 24, and lubricant injectors 26. Pump 12 is connected to reservoir 14 by supply line 18. Mechanical vent valve 16 is connected to pump 12 by pump line 20, and mechanical vent valve 16 is connected to reservoir 14 by return line 22. Mechanical vent valve 16 is connected to lubricant injectors 26 by lubrication line 24.

Lubrication system 10 is a dedicated lubrication assembly for use with lubricated machinery such as pumps, pistons, seals, bearings, and/or shafts. Reservoir 14 holds lubricant fluid for distribution to lubricant injectors 26 for lubricating the lubricated machinery. Pump 12 draws lubricant fluid from reservoir 14 through supply line 18. Pump 12 delivers lubricant fluid under pressure to lubricant injectors 26 through pump line 20, mechanical vent valve 16, and lubrication line 24. Each lubricant injector 26 is configured to fire once the lubricant fluid in lubrication line 24 has reached a predetermined level. When the lubricant fluid in lubrication line 24 reaches the predetermined level, lubricant injector 26 fires and dispenses lubricant fluid to the lubricated machinery. When all lubricant injectors 26 have fired, pump 12 continues to feed lubricant fluid to lubrication line 24, building pressure in lubrication line 24. Pressure continues to build in lubrication line 24 until the pressure of the lubricant fluid reaches a predetermined dump pressure level.

Once the pressure in lubrication line 24 reaches the dump pressure level, mechanical vent valve 16 shifts from a first state to a second state, to reset lubrication system 10. With mechanical vent valve 16 in the second state, lubricant fluid vents from lubrication line 24 to reservoir 14 through mechanical vent valve 16 and return line 22. Lubrication line 24 vents lubricant fluid to reservoir 14, thereby decreasing the pressure in lubrication line 24, and once the pressure in lubrication line 24 has sufficiently decreased, mechanical vent valve 16 returns to the first state.

FIG. 2A is a cross-sectional view of mechanical vent valve 16 in a first operating state. FIG. 2B is a cross-sectional view of mechanical vent valve 16 in a second operating state. FIG. 2A and FIG. 2B are substantially similar and will be discussed together. Mechanical vent valve 16 includes valve body 28, sleeve 30, spool 32, spring 34, indicator 36, and reset circuit 38. Valve body 28 includes inlet port 40, lubrication line port 42, vent port 44, actuation port 46, reset control port 48, and indicator opening 50. Reset circuit 38 includes reset control line 52, reset check valve 54, and bypass 56, which includes bypass line 58, bleed line 60, restriction 62, safety line 64, and safety check valve 66. Spool 32 includes first end 68, second end 70, and body 72.

Pump line 20 connects to inlet port 40, lubrication line 24 connects to lubrication line port 42, and return line 22 connects to vent port 44. Spool 32 is slidably disposed within sleeve 30. Body 72 extends between and connects first end 68 and second end 70. Indicator 36 is attached to second end 70 of spool 32 and projects into valve body 28 through indicator opening 50. Indicator opening 50 sealingly surrounds indicator 36, and indicator 36 is slidable through indicator opening 50. Spring 34 is positioned within sleeve 30 between valve body 28 and second end 70 of spool 32.

Reset circuit 38 fluidly connects inlet port 40, actuation port 46, and vent port 44. Reset control line 52 is attached to reset control port 48, and reset control line 52 extends from reset control port 48 to bypass line 58. Reset control line 52 is also connected to actuation port 46. Reset check valve 54 is disposed within reset control line 52. Bypass line 58 extends from reset control line 52 downstream of actuation port 46, and bypass line 58 splits into bleed line 60 and safety line 64. Bleed line 60 extends from bypass line 58 to vent port 44, and contains restriction 62, which may be an adjustable restriction as discussed later. Safety line 64 also extends from bypass line 58 to vent port 44. Safety check valve 66 is disposed within safety line 64.

In FIG. 2A, spool 32 is shown in a first operating state. Pump line 20 connects pump 12 (shown in FIG. 1) to inlet port 40. During the first operating state, pump 12 supplies lubricant fluid from reservoir 14 (shown in FIG. 1) to lubricant injectors 26 by pumping the lubricant fluid through pump line 20, inlet port 40, sleeve 30, lubrication line port 42, and lubrication line 24. First end 68 and second end 70 of spool 32 are sealingly disposed within sleeve 30, and second end 70 prevents the lubricant fluid that is passing through sleeve 30 from flowing to vent port 44.

Lubricant injectors 26 fire once the pressure in lubrication line 24 reaches a predetermined level for each lubricant injector 26. After each lubricant injector 26 has fired, pump 12 continues to supply lubricant fluid to lubrication line 24, thereby continuing to build pressure within lubrication line 24. Reset check valve 54 is disposed within reset control line 52 to prevent pressurized lubricant fluid from engaging spool 32 before the pressure in lubrication line 24 has reached the dump pressure. Reset check valve 54 is preferably an adjustable check valve that a user may set to open at the user's desired dump pressure. The dump pressure is preferably a pressure level that is sufficiently higher than the pressure required to fire all lubricant injectors 26 in lubricant system 10, to ensure that all lubricant injectors 26 have fired before reset check valve 54 opens to begin a system reset. The pressure in lubrication line 24 continues to build until the pressure reaches the dump pressure. Once the pressure of lubricant fluid reaches the dump pressure, reset check valve 54 opens, thereby allowing lubricant fluid to flow to reset circuit 38.

In FIG. 2B, spool 32 is shown in a second operating state. After the dump pressure has been reached, reset check valve 54 opens, thereby allowing lubricant fluid to flow through reset circuit 38. When reset check valve 54 opens, lubricant fluid enters reset circuit 38 through reset control port 48. A portion of the lubricant fluid flows through reset control line 52 to actuation port 46 and engages first end 68 of spool 32. Lubricant fluid also flows through reset control line 52 to bypass 56. The lubricant fluid in bypass 56 flows through bypass line 58 and to bleed line 60 and safety line 64, but safety check valve 66 prevents the lubricant fluid from flowing through safety line 64 to vent port 44.

The pressurized lubricant fluid flows through actuation port 46 and engages first end 68 of spool 32. As described above, bleed line 60 includes restriction 62, which ensures that there is sufficient pressure within reset circuit 38 for the lubricant fluid to actuate spool 32 from the first state to the second state, while allowing lubricant fluid in reset circuit 38 to return to reservoir 14 through vent port 44 and return line 22. The lubricant fluid is sufficiently pressurized to overcome the tension that spring 34 exerts on spool 32, and spool 32 is actuated to the second state.

Bleed line 60 is configured to allow a back-pressure to build within reset circuit 38. Bleed line 60 also allows some lubricant fluid to pass through bleed line 60 to vent to reservoir 14 through vent port 44. Thus, pump 12 may continue to run without a buildup of excess pressure in reset circuit 38 because lubricant fluid will vent through bleed line 60.

Safety check valve 66 is configured to prevent lubricant fluid from freely flowing through safety line 64 from bypass line 58 to vent port 44. However, if the back-pressure built up within reset circuit 38 reaches a maximum system pressure (i.e. the maximum pressure that reset circuit 38 may safely handle before failure) then safety check valve 66 opens to relieve pressure within reset circuit 38 by allowing lubricant fluid to freely flow from reset circuit 38 to vent port 44 through safety line 64, and on to reservoir 14.

In the second state, first end 68 of spool 32 is sealingly disposed within sleeve 30 between inlet port 40 and lubrication line port 42. In this way, the lubricant fluid pumped into mechanical vent valve 16 through inlet port 40 must travel through reset circuit 38 to vent port 44. Additionally, with spool 32 in the second state, lubrication line 24 is fluidly connected to reservoir 14 via lubrication line port 42, sleeve 30, vent port 44, and return line 22. Thus, the pressurized lubricant fluid in lubrication line 24 vents to reservoir 14 through mechanical vent valve 16.

As spool 32 transitions to the second state, indicator 36 slides through indictor opening 50 and projects out of valve body 28. In this way, indicator 36 gives the user a visual indication that the pressure of lubricant fluid in lubricant system 10 has reached the dump pressure, which informs the user that all lubricant injectors 26 have fired. Once the user receives the visual indication that all lubricant injectors 26 have fired, the user may turn off pump 12, which allows lubricant system 10 to complete reset. While lubricant system 10 has been described such that the user deactivates pump 12, it is understood that pump 12 may be set to run on a timer, pump 12 may be deactivated by indicator 36 engaging pump 12 after indicator 36 projects from valve body 28, or pump 12 may be deactivated in any other suitable manner.

The back-pressure within reset circuit 38 is too great for spool 32 to immediately return to the first state after pump 12 is deactivated. The lubricant fluid in reset circuit 38 flows through bleed line 60 to vent port 44, and from vent port 44 through to reservoir 14. Bleed line 60 with restriction 62 thereby allows the back-pressure within reset circuit 38 to sufficiently degrade such that spring 34 returns spool 32 to the first state. FIGS. 3-5 illustrate embodiments of adjustable restrictions that may be employed in bleed line 60 as restriction 62.

FIG. 3 is a cross-sectional view of one embodiment of an adjustable restriction. Adjustable restriction 162 is a restriction within a restricted line, such as bleed line 60. In this embodiment, adjustable restriction 162 includes piston 174, stop 176, bleed path 178, and length of engagement 180. Bleed line 60 defines bore 182, and bleed line 160 includes fluid inlet 184 and fluid outlet 186.

Piston 174 is disposed within bore 182. Bleed path 178 is defined by a clearance between piston 174 and bore 182. Length of engagement 180 is defined by a length of piston 174 fully encased by bleed line 160. Stop 176 protrudes into a flowpath of bleed line 60 downstream of piston 174. While stop 176 is shown as a plug projecting from an endwall of bleed line 60, it is understood that stop 170 may be a grate within bleed line 60, a bar extending across a diameter of bleed line 60, or any other configuration suitable for maintaining length of engagement 180 between piston 174 and bleed line 60.

Pressurized lubricant fluid enters bleed line 60 from an upstream system through fluid inlet 184. The lubricant fluid flows through bleed path 178, and the lubricant fluid exits bleed line 60 downstream of adjustable restriction 162, through fluid outlet 186. Piston 174 prevents the pressurized fluid from freely flowing through bore 182 to fluid outlet 186. Instead, the pressurized fluid must flow through bleed path 178 around piston 174 to fluid outlet 186. Adjustable restriction 162 thereby builds back-pressure within the upstream system, while still allowing a portion of the pressurized lubricant fluid to bleed downstream through bleed path 178 and fluid outlet 186. When pressurized lubricant fluid enters adjustable restriction 162 and engages piston 174, the pressurized lubricant fluid pushes piston 174 downstream within bore 182. Stop 176 engages piston 174 to ensure that piston 174 remains disposed within bore 182 and that length of engagement 180 is maintained.

A certain pressure is required to cause a fluid to flow through a restricted flow path, such as bleed path 178. If bleed path 178 is too great, then the system will not be able to build sufficient system pressure, and the fluid will freely flow from fluid inlet 184 to fluid outlet 186 through bleed path 178. However, if bleed path 178 is too small, then the pressure within the upstream system will not degrade beyond a set level, because the pressure within the system will be insufficient to force additional fluid through adjustable restriction 162. Bleed path 178 and length of engagement 180 allow a user to ensure that adequate back-pressure will build within the upstream system, while also ensuring that the pressure will degrade to a desired level after pressure stops being applied to the upstream system. Where a different pressurized lubricant fluid is utilized or the user desires a different back-pressure or minimum pressure, piston 174 may be replaced with various other pistons to alter length of engagement 180 and bleed path 178.

FIG. 4 is a cross-sectional view of another embodiment of an adjustable restriction, which may function as restriction 62 within bleed line 60. In the present embodiment, adjustable restriction 262 includes piston 274, bleed path 278, length of engagement 280, and spring 288. Bleed line 60 includes fluid inlet 284, fluid outlet 286. Additionally, bleed line 60 defines upstream bore 290 and downstream bore 292, and bleed line 60 includes end wall 294.

Piston 274 is disposed within upstream bore 290. Bleed path 278 is defined by a clearance between piston 274 and upstream bore 290. Upstream bore 290 is within a portion of bleed line 60 disposed upstream of fluid outlet 286. Downstream bore 292 is within a portion of bleed line 60 disposed downstream of fluid outlet 286. Length of engagement 280 is defined by a length of piston 274 fully within upstream bore 290. Spring 288 is secured to end wall 294 of bleed line 60, and spring 288 is attached to piston 274.

Pressurized lubricant fluid enters adjustable restriction 262 from an upstream system through fluid inlet 284. The lubricant fluid flows through bleed path 278 and exits adjustable restriction 262 through fluid outlet 286. Piston 274 prevents the pressurized fluid from freely flowing through upstream bore 290 to fluid outlet 286. Instead, the pressurized fluid must flow through bleed path 278 to fluid outlet 286. Adjustable restriction 262 thereby builds back-pressure within the upstream system, while still allowing a portion of the pressurized lubricant fluid to flow downstream through bleed path 278 and fluid outlet 286.

When pressurized lubricant fluid enters adjustable restriction 262 and engages piston 274, the pressurized lubricant fluid pushes piston 274 downstream within upstream bore 290 and towards downstream bore 292. The tension in spring 288 maintains length of engagement 280 under low-pressure conditions. As the pressure increases, piston 274 shifts downstream over fluid outlet 286 and into downstream bore 292. As piston 274 shifts into downstream bore 292, length of engagement 280 decreases, and adjustable restriction 262 becomes less restrictive, which allows pressurized lubricant fluid to pass through bleed line 60 at a greater flow rate. As the pressure within the upstream system is relieved, spring 288 pushes piston 274 back into an original position within upstream bore 290, and length of engagement 280 is restored to an initial length of engagement.

Thus, this embodiment of adjustable restriction 262 prevents accelerated pressure decay within the upstream system when the upstream system is in a low-pressure state. Adjustable restriction 262 also allows for accelerated pressure decay within the upstream system when the upstream system is in a high-pressure state. Adjustable restriction 262 is self-cleaning due to piston 274 oscillating within upstream bore 290 and downstream bore 292. As piston 274 shifts downstream, fluid soaps or particles that had built up within bleed path 278 are dislodged and carried downstream through fluid outlet 286 by the pressurized lubricant fluid.

FIG. 5 is a cross-sectional view of another embodiment of an adjustable restriction. Adjustable restriction 362 functions as a restriction within a restricted line, such as restriction 62 within bleed line 60. In this embodiment, adjustable restriction 362 includes piston 374, bleed path 378, length of engagement 380, and spring 388. Bleed line 60 includes fluid inlet 384, fluid outlet 386 and flange 394. Bleed line 60 defines first bore 396 and second bore 398.

Piston 374 is partially disposed within second bore 398. Bleed path 378 is defined by a clearance between piston 374 and second bore 398. Length of engagement 380 is defined by a length of piston 374 disposed within second bore 398. Flange 394 extends into bleed line 60 at a downstream end of second bore 398, and spring 388 is positioned within bleed line 60 between flange 394 and piston 374. First bore 396 has a greater diameter than second bore 398.

Pressurized lubricant fluid enters first bore 396 from an upstream system through fluid inlet 384. The lubricant fluid flows through bleed path 378 and second bore 398, and the lubricant fluid exits adjustable restriction 362 through fluid outlet 386. Piston 374 prevents the pressurized fluid from freely flowing through second bore 398 to fluid outlet 386. Instead, the pressurized fluid must flow through bleed path 378 to fluid outlet 386. Adjustable restriction 362 thereby builds back-pressure within the upstream system, while still allowing a portion of the pressurized lubricant fluid to flow downstream through bleed path 378 and fluid outlet 386.

Adjustable restriction 362 has a length of engagement 380 that increases as the pressure within the upstream system increases. A certain pressure is required to cause a fluid to flow through a restriction, such as bleed path 378. If bleed path 378 is too great, then the system will not be able to build sufficient system pressure, the fluid will freely flow from fluid inlet 384 to fluid outlet 386 through bleed path 378. However, if bleed path 378 is too small, then the pressure within the upstream system will not degrade beyond a set level, because the pressure within the system will be insufficient to force additional fluid through adjustable restriction 362. Bleed path 378 and length of engagement 380 ensure that adequate back-pressure will build within the upstream system, while also ensuring that the pressure will degrade to a desired level after pressure stops being applied to the upstream system. As the pressure in the upstream system increases, piston 374 is pushed into second bore 398, thereby increasing length of engagement 380. Thus, length of engagement 380 increases as the pressure in the upstream system increases, providing more restriction. As the pressure in the upstream system decreases, length of engagement 380 decreases, allowing the pressurized fluid to bleed through adjustable restriction 362 more efficiently. In this way, adjustable restriction 362 ensures that the system builds an adequate back-pressure for fluids with a range of viscosities and pressures and that the system will bleed efficiently, because length of engagement 380 will vary accordingly. Although piston 374 is described as projecting into first bore 396 in an initial state, it is understood that piston 374 may project directly into the upstream system.

After pressure is no longer applied to the upstream system, such as when pump 12 (shown in FIG. 1) is shut off, the pressure in the upstream system bleeds through bleed path 378 to allow the upstream system to return to an initial state. As pressurized lubricating fluid flows through bleed path 378, the upstream pressure degrades. As the upstream pressure degrades, spring 388 pushes piston 374 out of second bore 398 and into first bore 396, thus returning piston 374 to an initial state. As piston 374 returns to the initial state, length of engagement 380 decreases, thereby requiring less pressure to bleed the lubricant fluid through bleed path 378. Additionally, a shorter length of engagement 380 allows the system pressure to degrade at a higher rate, and the shorter length of engagement 380 also ensures that system pressure will degrade to a level that allows the upstream system to return to the initial state.

Thus, adjustable restriction 362 builds adequate back-pressure within the upstream system for fluids with a range of viscosities and pressures. Adjustable restriction 362 also allows for accelerated pressure decay within the upstream system once the upstream system has begun to bleed pressure to return to an initial state. Additionally, piston 374 oscillating within second bore 398 causes adjustable restriction 362 to be self-cleaning. As piston 374 oscillates within second bore 398, fluid soaps or particles that had built up within bleed path 378 are dislodged and carried downstream through fluid outlet 386 by pressurized lubricant fluid.

The mechanical vent valve 16 described herein provides several advantages. Mechanical vent valve 16 provides a simple venting solution for lubrication system 10, and mechanical vent valve 16 eliminates the need for pressure switches, cables, or solenoids and controllers in injector-based systems, thereby providing lower system cost to the end user.

Indicator 36 described herein provides several advantages. Remote indication of mechanical vent valve 16 shifting from a first state to a second state, and thereby draining lubrication line 24 gives the end user confirmation, through visual verification or a proximity sensor, that lubricant injectors 26 have surpassed the pressure at which the lubricant injectors 26 theoretically fire. This informs the user that pump 12 is no longer providing pressure to lubrication line 24. Additionally, indicator 36 informs the end user that pump 12 may be shut down, which allows lubricant system 10 to reset for the next lubrication cycle.

Mechanical vent valve 16 also allows for lubricant fluid to circulate through pump 12, mechanical vent valve 16, and reservoir 14 after lubricant injectors 26 have fired, but before lubricant system 10 is reset. After spool 32 has shifted to the second state, pump 12 remains in continuous operation, and the lubricant fluid supplied to mechanical vent valve 16 from pump 12 is routed through bleed line 60 and back to reservoir 14. Recirculating the lubricant fluid enhances the performance of lubricant system 10. Recirculating lubricant fluid allows pump 12 to run continuously after lubricant injectors 26 have fired, without the possibility that lubricant injectors 26 will re-fire, causing over- lubrication, or that lubricant system 10 will be over-pressurized due to continuous pump 12 operation. Recirculating the lubricant fluid also allows the user to set pump 12 to operate for a set period of time, after which all lubricant injectors 26 should have theoretically fired. Additionally, the lubricant fluid is maintained in a dynamic state, which allows lubricant system 10 to maintain a higher lubricant fluid temperature and a consistent lubricant fluid viscosity. Maintaining a higher working temperature and a constant viscosity for the lubricant fluid allows the mechanical vent valve 16 to quickly rest and to be actuated repeatedly, without the need to wait for the lubricant fluid to warm up.

The restrictions described herein provide several advantages. The length of engagement is adjustable, which allows the restrictions to function effectively across all fluid viscosities and pressures.

Adjustable restriction 262 prevents accelerated system decay by restricting the fluid flow rate under low-pressure system conditions, thereby allowing for proper system operation. Adjustable restriction 262 also allows for accelerated system decay under high-pressure system conditions, due to the self-adjusting nature of adjustable restriction 262. Furthermore, adjustable restriction 262 functions as a self-cleaning restriction, due to the dynamic movement of piston 274 during operation. Adjustable restriction 262 also allows for pressure decay within the system without the need for metal-to-metal contact. Adjustable restriction 262 also allows for restricted pressure decay during system vent and for accelerated pressure decay during system reset.

The adjustable restriction 362 described herein additionally provides several advantages. The amount of restriction provided by adjustable restriction 362 increases during system pressurization and decreases during system depressurization. The increase and decrease in restriction allows for adjustable restriction 362 to function across a wide range of fluid viscosities and pressures. Adjustable restriction 362 also allows for pressure degradation during system reset, because the amount of restriction decreases as system pressure decreases. Moreover, adjustable restriction 362 functions as a self- cleaning restriction, due to the dynamic movement of piston 374 during operation.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.