Airless reversible spray tip

Details Airless reversible spray tip Airless reversible spray tip

1999-09-29

2001-07-24

Morris, Lesley D. (Department: 3752)

Fluid sprinkling, spraying, and diffusing

With cleaning means, drip collecting, waste disposal or soil...

Nozzle cleaner, flusher or drainer

C239S071000

Reexamination Certificate

active

06264115

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to spray tip assemblies for airless, high pressure spraying, and more particularly to reversible spray tip assemblies provided with a tip guard for safety.
2. Description of the Related Art
Reversible spray tip assemblies are widely used for high pressure, airless spraying of paint and other fluids. In a typical reversible spray tip assembly, a small spray nozzle is carried in a cylindrical, rotatable nozzle carrier. The nozzle carrier can be rotated 180 degrees, thereby reversing the direction of paint flow through the nozzle for cleaning nozzle obstructions. Typically the nozzle carriers are interchangeable with other nozzle carriers carrying nozzles of various diameters and capacities. Prior reversible spray tip assemblies, although successful, continue to be plagued by several problems which affect their convenience, safety and utility.
Safety for the user is a primary concern. Airless high pressure sprayers eject a very high velocity, narrow jet, which disperses and slows as it atomizes. In the area near the nozzle (within approximately one inch), where the jet is most narrow and has highest velocity, there is a risk of injection injuries to a user. In recognition of this risk, prior sprayers have included various styles of spray guards to prevent the user's body from being hit by the spray jet near the spray nozzle orifice and to warn the user of the hazard.
While such spray guards reduce the risk of injection, prior spray guards have generally suffered from a tendency to accumulate paint during spraying. Accumulated paint can then drip from the guard, creating a mess and potentially staining clothing or surfaces in the work area. In addition, accumulated paint can be splattered from the tip guard by the aerodynamic forces of the spray, causing imperfections on the painted surface. When this occurs, the user may be tempted to remove the spray guard, thereby risking injury for the sake of convenience.
Some efforts have been made to reduce the tendency for the spray guard to accumulate paint. For example, U.S. Pat. No. 4,685,621 to Scherer et al. (1987) features a tip guard having two pairs of vanes extending forward and radially outward from a base, each pair of vanes joined by a crossbar. Scherer's tip guard allows air flow through the side of the spray guard, and is somewhat successful in reducing buildup of paint on the spray guard. Nevertheless, the accumulation of paint from overspray is not completely eliminated by Scherer's design, and users may still be tempted to remove the spray guard.
Another approach to the problem is taken by Eull in his U.S. Pat. No. 4,165,836 (1979). This patent describes a safety tip guard which is coupled to the sprayer in such a way that the spray tip will not operate if the tip guard is removed. This approach improves the safety of the spray guard, but paint can still accumulate and drip. In addition, the user may be forced to stop to wipe the spray guard occasionally; if the sprayer is actuated while the user has positioned fingers inside the guard for wiping, injection injury could result.
While prior attempts to improve the spray guard have improved the situation to some degree, none of the prior guards is considered convenient, safe and trouble free.
A related problem with existing reversible tip spray tips arises from their reversible tip feature. It is a major benefit of such devices that a user can easily rotate the spraying nozzle into a reverse flow position. This enables the user to quickly remove any particles that have plugged the very small orifice in the spray tip, by injecting paint through the spray tip in the reversed flow direction, dislodging the obstruction. However, with existing reversible tip devices it is possible to accidentally rotate the spray tip out of position if the tip handle gets bumped in the course of handling or moving the spray gun. It is also possible for a user to fail to rotate the spray tip completely into position before activating the sprayer. Either of these circumstances can yield a condition where the tip is not properly aligned when fluid pressure is applied, which can result in accidents ranging in severity from minor nuisance to serious injury or damage.
Prior reversible spray tips commonly include rotation stops, so that the tip cannot be overrotated inadvertently. For example, U.S. Pat. No. 4,165,836 to Eull (1979) includes a handle with a shoulder. The shoulder has a partially rounded shape to permit tip rotation and a flattened portion which contacts a flange to limit the range of rotation. While it does prevent overrotation, the flattened portion of the shoulder does not prevent improper positioning by underrotation of the tip. Other tips similarly limit the range of rotation but do not positively lock the tip into position. Thus, prior spray tips do not completely solve the problem of inadvertent tip misalignment.
In addition to misalignment problems, prior reversible spray tips are subject to “spitting” and dripping problems when the spray gun is being triggered on or off. These problems are related to the seal design. For sealing the rotatable metal cylinder, a floating cylinder seal is commonly provided with a forward sealing face that conforms with the outer cylindrical contour. High pressure tends to force the floating seal into sealing engagement with the cylinder during spraying, preventing leakage.
To prevent leakage during start up conditions, an initial compressive loading is typically applied to the seal. For example, in the U.S. Pat. No. 4,715,537 to Calder (1987), the floating seal is biased by a spring to provide initial sealing pressure during start up. The floating seal is sealed against leakage from its rearward face by an annular (O-ring) seal.
Existing seals exhibit, in varying degrees, a tendency to cause a “spit” or drip from the spray nozzle, particularly when pressure is suddenly removed. Moreover, these seals in many cases are difficult to assemble in proper alignment, as is necessary for an effective seal. Some existing tips have a further problem: when the rotatable metal cylinder is partially rotated out of alignment with the fluid supply port, seal leakage can occur due to the paint “bridging” the seal between the port and an outside surface. This troublesome “bridging” situation is illustrated by FIG.
1
. This figure shows the position of the nozzle carrier
1
when it has been turned partially so that the nozzle axis
2
does not align with the longitudinal axis
3
of the fluid passage
4
. If the dimension w
o
is not sufficiently narrow to be fully covered by the concave face
5
of the piston seal
6
while in this intermediate position, the seal formed by the contact between the concave face
5
and the nozzle carrier
1
is bridged, and fluid (symbolized by flow line
7
) is allowed to escape by flowing around the concave seal face
5
. Therefore, to prevent bridging the seal, the arc defined by the opening of the rear nozzle carrier orifice
8
must be smaller than the arc defined by the concave seal face
5
. This limitation is defined by a complex relationship, but for small concave faces (as used for practical sealing faces) and assuming that the fluid passage
4
is centered in the piston seal
6
, it is sufficient to prevent bridging if the width w
o
is less than (d
ps
−w)/2, where w is the width of the fluid passage
4
, d
ps
is the outside diameter of the piston seal
6
, and w
o
is the width of the rear orifice in the spray nozzle carrier
1
.
Prior reversible spray tips have had problems related to the manner of retaining a spray nozzle
9
in the rotatable cylindrical spray nozzle carrier
1
. Typically, a small tungsten carbide spray nozzle is installed in a transverse bore of the nozzle carrier
1
, so that the axis of the nozzle is perpendicular to the axis of the nozzle carrier
1
. The transverse bore of the carrier
1
has a small step or bevel
10
which limits movement of the spray nozzle in the forward direction. A re

Affiliated with

Also associated with

Rating

Airless reversible spray tip does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Airless reversible spray tip, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Airless reversible spray tip will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2478946