Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B11/00—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation
  • F04B11/005—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation using two or more pumping pistons
  • F04B11/0058—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation using two or more pumping pistons with piston speed control
  • F04B11/0066—Equalisation of pulses, e.g. by use of air vessels; Counteracting cavitation using two or more pumping pistons with piston speed control with special shape of the actuating element
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B1/00—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders
  • F04B1/02—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders having two cylinders
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B23/00—Pumping installations or systems
  • F04B23/04—Combinations of two or more pumps
  • F04B23/06—Combinations of two or more pumps the pumps being all of reciprocating positive-displacement type

Definitions

• a myriad of different types of pumps are known for use in pumping various materials.
• the number of choices of pumps suitable for such applications drops substantially, particularly when it is desired to pump such materials at relatively elevated pressures and/or at predetermined flow rates.
• reciprocating piston pumps have been widely used in such applications, such pumps suffer from having pulses in the pressure output of the pumps during piston reversal.
• Such pumps also suffer to a certain extent from leakage and seepage of pumped material past the seals which is particularly critical when the material is air- sensitive such as isocyanates. This leakage is in both directions and can cause environmental contamination, pumped fluid contamination and regenerative abrasive wear damage to the pump.
• the reduction and/or elimination of pulses in the output is particularly important for circulating systems, fine spray applications and proportional metering to produce constant output.
• Centrifugal pumps are capable of pumping abrasive materials without pressure pulses but suffer from the problems of not being positive displacement type (flow rate is not directly related to speed), inefficiency, shaft seal leakage and impose a high degree of shear on materials which may be shear-sensitive.
• Gear pumps are commonly used for metering and proportioning apparatus due their ease in synchronizing with other pumps. Such products, however, are ill-suited for pumping of abrasive materials which cause unacceptable wear.
• «_ invention to provide such a pump which has leak-proof operation to avoid contamination of the environment in which the pump is located or contamination of the pumped fluid by the environment.
• a multi-piston/cylinder pump is driven by a cam.
• the use of pistons in conjunction with diaphragms allows a much higher pressure output , capability that a simple diaphragm pump and a more positive displacement action than diaphragm pumps.
• the cam is powered by a DC motor or other type of conventional variable speed rotary driving mechanism (electric, hydraulic or the like). When used with these drives, the pump can be stalled against pressure just like a typical air-operated reciprocating piston pump. This mode allows adjustable constant flow.
• a constant speed motor driving the pump would use a pressure switch to turn the motor on and off. Because the motion input to the pump is rotary, it can be easily synchronized with another pump(s) to provide a plural component material proportioning system or with a conveyor to more fully automate production.
• the cam profile is designed so that the reciprocating pistons (which alternate between pumping and intake strokes) have a net velocity sum of their pumping strokes which is generally constant. By doing so, one essentially can eliminate pressure losses that create pulses which result from the piston reversal of a conventional piston pump.
• two pistons are used although it can be appreciated that more pistons may be used if desired.
• intake flow is controlled by check valves which typically take a discreet amount of time to seat. Fluid can flow backwards during this time causing small pump output pressure variations during the valve seating but such can be compensated for by shaping the cam profile to provide a nearly totally pulseless operation.
• Each piston is sealed in its respective cylinder by a relatively conventional type seal mechanism. Attached to the piston on the low pressure intake side of the seal is a diaphragm which serves to isolate the fluid from the environment and assure a leak proof device. As used in this application, the term “diaphragm” is understood to include membranes, bellows or other such structures performing a similar function.
• An intake passage provides flow directly over the piston between the main seal and the diaphragm to prevent the build-up and hardening of material in the intake section and on the piston. The intake flow then passes through the intake check and into the pumping chamber and then exits through an outlet passage which also has a check valve. This flow path minimizes stagnant areas of non-flowing fluid where fluids may settle out and/or harden.
• the passage is oriented to minimize air entrapment and continually replenish the fluid in the intake area.
• the cam can either be of a push-pull type, that is, where the roller rides in a track or can be a conventional outer profile cam wherein the piston assembly roller is spring loaded against the cam to maintain it in position.
• Figure 1 is a general cross section of the pump of the instant invention.
• Figure 2 is a cross section taken along 2-2 of Figure 1 showing the cam of the instant invention.
• Figure 3 is an alternate embodiment of the cam of Figure 2.
• Figure 3a is a chart showing the velocities and outputs of a two piston pump.
• the pump of the instant invention is comprised of a main housing 12 in which runs a shaft 14 having a gear 16 mounted thereon.
• a motor (not shown) which may be a DC brushless type motor, drives gear 16 and shaft 14 to turn cam 18 mounted on the end thereof.
• a cam follower assembly 20 rides on cam 18 and is comprised of a follower housing 22 having a follower 24 mounted thereto via shaft 26.
• follower housing 22 has guide rollers 28 mounted on the outside thereof which run in slots 30 in housing 12.
• follower assembly 20 is spring loaded against cam 18 by means of a spring 32.
• Follower assembly 20 is attached to a piston 34 and located in between follower 22 and piston 34 is a diaphragm 36. Those three parts are fastened together by a bolt 38 which passes consecutively therethrough.
• An initial inlet passage 40 leads into a flushing chamber 42 located about piston 34 between diaphragm 36 and main pressure seal 44 in cylinder 46. Flushing chamber 42 runs circumferentially around piston 34 thus inlet flow therethrough serves to flush material through which might potentially harden off the surface of piston 34. Inlet flow thence passes through passage 48 in to main inlet passage 50 which has located in series therein a check valve 52 of a conventional nature.
• Pumping chamber 54 is located in the end of cylinder 46 over piston 34 and also has connected thereto outlet passage 56 having an outlet check 58 of conventional design therein.
• outlet passage 56 having an outlet check 58 of conventional design therein.
• diaphragm 36 flexes fipwardly to the point of nearly touching the upper surface 42a of flushing chamber 42 thereby continually assuring a fresh * flow of material through the pump and the prevention of stagnant flow zones therein.
• Such a type of cam is often referred to as a desmodromic type cam, and an example of such a cam is shown in Figure 3 wherein the roller is guided in a track 60 and is driven in both its pumping and intake strokes.
• seal 44 may be of any conventional type which is capable of performing a proper sealing function, however, it can be appreciated that because diaphragm 36 is subjected to relatively low pressures, its service life will be dramatically increased to maintain the pump in a substantially leak-free state. It can also be seen that if seal 44 should leak, its leakage is from the high pressure side back into the inlet rather than into the environment.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Reciprocating Pumps (AREA)

Applications Claiming Priority (3)

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Citations (4)

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• 1990
  • 1990-07-05 JP JP51127890A patent/JPH05501138A/ja active Pending
  • 1990-07-05 EP EP90912068A patent/EP0486556B1/de not_active Expired - Lifetime
  • 1990-07-05 WO PCT/US1990/003786 patent/WO1991002158A1/en active IP Right Grant
  • 1990-07-05 DE DE69026945T patent/DE69026945T2/de not_active Expired - Fee Related

Patent Citations (4)

Non-Patent Citations (1)

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