Pumps – Expansible chamber type – Having pulsation dampening fluid receiving space
Reexamination Certificate
1997-10-17
2001-02-06
Freay, Charles G. (Department: 5746)
Pumps
Expansible chamber type
Having pulsation dampening fluid receiving space
C239S332000, C137S541000
Reexamination Certificate
active
06183224
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to airless paint sprayers, and more particularly, to a mechanism for providing a more consistent spray of paint without a loss of pressure over a range of operating parameters.
In a typical airless paint sprayer, a piston driven diaphragm pulls the paint from a supply line into a paint holding or diaphragm chamber. A spray gun has a trigger which, when depressed, opens a valve to allow the pressurized paint in the chamber to flow to a gun nozzle and atomize as it exits a paint orifice for spraying onto a surface to be coated.
Airless paint sprayers commonly include a suction tube inserted within a can of paint through which the paint is delivered to the diaphragm chamber. Suction is created in the suction tube by a deformable diaphragm which is secured around its perimeter. A central portion of the diaphragm is oscillated, by a piston-driven hydraulic system, for example, between a convex and a concave configuration to thereby pull the paint toward the diaphragm and hence force it outwardly to the spray gun.
In another format, a rotating eccentric cam drives a bearing which in turn drives a piston. The piston is coupled to the diaphragm and the rotation of the cam drives the piston to thereby move the diaphragm to and between the convex and concave configurations. The paint is drawn from the can through the suction tube and inlet valve toward the diaphragm and into the diaphragm chamber to be discharged through the spray gun.
Despite past efforts, the use of such systems for spraying paint, for example, have been subject to inconsistent results and unexplained, undesirable variations. For example, on a given day, a system may not work well with one paint, failing to fully atomize it and “spattering” it onto a surface while operating efficiently with the same paint at another time or in another location.
Other problems which are commonly identified in such airless paint sprayers include ineffective spraying of paint of a first type but efficient spraying of paint of a second type. Several possible causes of problems of this type have been proposed such as lack of consistent priming, paint buildup, clogged filters, paint viscosity, humidity, etc. However, these problems occur even when a problem paint is thinned to the general consistency of water, the filters are clean, or the flow path of the paint unclogged. These symptoms can even be apparent in using one paint while not in using another even though the paints have similar viscosities.
Accordingly, the effective and consistent use of an airless paint system appears to be a sometimes thing dependent on a variation of parameters, ever changing.
Therefore, it is apparent that there is a need for an airless paint sprayer which does not exhibit a loss of pressure while spraying and can reliably, efficiently and effectively spray all types of paint at a wide range of operating conditions without the above identified problems and inconsistencies.
It has thus been a primary objective of this invention to provide an improved airless paint sprayer which does not loose pressure while spraying.
It has been a further objective of this invention to provide such a paint sprayer which can be efficiently and effectively used with a variety of paint types without loosing pressure while spraying.
It has been a still further objective of this invention to provide such a paint sprayer which can be used with a variety of paints and paint viscosities to consistently atomize and spray the paint in a desired homogeneous pattern.
SUMMARY OF THE INVENTION
To these ends, a preferred embodiment of the invention contemplates the use of a dampener on the spray liquid or paint intake side of the paint sprayer.
One aspect of the invention is the realization of the basic problem which is responsible for inconsistent paint spraying performance. According to the invention, that problem is the inconsistency of the system by which paint is delivered from an open container to the pumping or diaphragm chamber of the spraying apparatus.
Typically the suction tube between the inlet check valve of the pumping chamber and the open paint container is vertically oriented and may be 1 to 2 feet long. Paint is sucked up from the container in this tube, through the inlet check valve and into the pumping chamber. In order to suck the paint past the inlet check valve the diaphragm must create a pressure drop in the chamber and it does so by virtue of its eccentric drive or by the piston-driven hydraulic drive. The nature of the diaphragm is cyclical; the diaphragm constantly accelerating and decelerating through each sucking and pumping direction.
For example, as the diaphragm is moved to enlarge the chamber for sucking paint up the supply tube, it accelerates due to the eccentric action of the piston. It decelerates as it reaches its maximum stroke and the check valve closes. During this time, the paint in the tube is subjected to a pressure drop which first accelerates then decelerates to near equilibrium when the inlet check valve closes. Thereafter, the diaphragm is accelerated into the chamber to pump out the paint therein. Once this stroke ends, the diaphragm accelerates in a reverse direction to again open the inlet check valve and suck paint up from the tube. Thus, the eccentric rotation of the cam drive and the acceleration/deceleration of the rod following the cam create acceleration spikes in the flow of the paint during each cycle. The acceleration spikes correspond to specific points or areas on the drive cam which result in significant acceleration/deceleration of the rod. These acceleration/deceleration forces are transferred from the rod to the diaphragm thereby resulting in acceleration spikes in the flow of the paint drawn into the diaphragm chamber through the inlet check valve and suction tube. The paint is thus being accelerated and decelerated with each stroke of the diaphragm. According to this invention, it is believed that the force required to accelerate the paint was in many instances greater than the paint itself could support without cavitation or boiling.
Accordingly, it has been discovered that the paint was cavitating or boiling in the diaphragm chamber in many instances due to the sum of the various forces to which the paint is subjected. Factors which contribute to paint cavitation in such paint sprayers are the ambient temperature and barometric atmospheric pressure (i.e., altitude) at which the sprayer was operated. Other factors which may contribute are the dimensions, configurations and tolerances of the suction tube, and the viscosity of the paint. Thus, under specific conditions, it has now been discovered that the force required to overcome the inertia of the paint and accelerate it through the system was greater than the paint could support. This resulted in the cavitation or boiling of some of the liquids in the paint, and the resulting interruption of full paint flow through the sprayer, a loss of pressure while spraying, and inconsistent spraying results, such as “spattering” and inconsistent atomization.
Accordingly, the dampener of one embodiment of the present invention comprises a generally T-shaped fitting connected to the suction tube leading to the inlet check valve of the pump or diaphragm chamber. The T-shaped fitting includes a first leg having a port through which paint is received from the suction tube inserted in the paint can or reservoir and a second leg perpendicular to the first leg through which paint is discharged via a second port to the inlet check valve of the pump. A third leg of the T-fitting comprises a closed chamber which is in line with the first leg and perpendicular to the second leg in a presently preferred embodiment of the invention. Other configurations of the dampener for different sprayer configurations are possible and within the scope of this invention.
The dampener of this invention solves a significant number of occurrences of the problem of pressure loss during the operation of the paint sprayer and the inability of the sprayer caused, in
Campbell Hausfeld/ Scott Fetzer Company
Freay Charles G.
Jones Day Reavis & Pogue
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