1. Field of the Invention
This invention relates to equipment for airless spraying of liquids and in particular to an improved spray tip assembly.
2. Brief Statement of the Prior Art
Airless spraying of liquids is a well established industry and is the predominately used method for professional spraying of paints and the like. The liquid is pressurized to relatively high pressures, e.g., 3,000 to about 5000 psi and is sprayed through a minute orifice formed of abrasive resistant materials, typically tungsten carbide.
The majority of the airless spray equipment uses a relatively low-cost orifice tip subassembly known as a "flat tip". The flat tip has a generally cylindrical case with a circular base and a small diameter through passageway in which is permanently seated a small orifice tip member. This construction efficiently minimizes the quantity of the relatively expense tungsten carbide required for the wear-resistent orifice tips.
One of the problems encountered in the airless spraying of liquids is that the minute diameter passageway in the orifice tip member tends to clog with debris or scale present in the liquid being sprayed. This tendency is combated to some extent by use of filters and careful preparation of the spraying liquid, however the problem is encountered sufficiently frequently that a reversible type of spray nozzles has been developed. These reversible spray nozzles typically contain the orifice tip member in a rotatable turret member which permits the position of the orifice tip member to be reversed so the spray liquid can be applied under high pressure to dislodge any obstructions from the orifice tip member.
Substantial improvements have been made in the design of the reversible tip spray heads, reducing their manufacturing costs and improving their use. One cost factor, however, which has not been significantly reduced is the relatively high cost of the custom orifice tips used in this construction. The orifice tips are formed of a wear-resistent material, usually tungsten carbide, and must be of sufficient size and configuration to be permanently mounted in the rotatable turret member.
A reversible spray head has recently been introduced to the market in which the rotatable cylindrical turret member is provided with a large internal recess to permit use of the comparatively inexpensive flat tips. This design utilizes a very large diameter counterbore in the turret member which receives the metal case of the flat orifice tip with an interlocking plug having an external surface contoured to the cylindrical wall of the rotatable turret member.
A difficulty with the aforementioned construction is that it significantly weakens the turret member. As previously mentioned, the spray heads are designed to spray liquids at high pressures, in excess of 3000 psi and any significant reduction in the wall thicknesses of the members renders them prone to stress failures.