This invention relates to an improvement in safety circuits for cleaning lances which utilize high pressure water, and which require a pair of trigger circuits to be held closed in order to direct the water against the surface to be cleaned.
In the prior art, high pressure water is often utilized to clean surfaces. As an example, paint, dirt and other sludge may be removed from a surface by jetting high pressure water out of a hand-held cleaning lance. Typically, the cleaning lances are provided with triggers which must be held closed in order for the high pressure fluid to be directed outwardly of the lance. If the trigger is released, then a mechanical connection within the lance moves to open a dump valve, and direct the high pressure water to a dump outlet at which it is allowed to leave the lance at a reduced pressure.
The trigger ensures the high pressure water is stopped when cleaning is to be interrupted, and also provides a safety benefit in that the lance must be held in the hand of a user with the trigger closed for the high pressure water to be directed outwardly of the lance. This reduces the likelihood of high pressure water being directed in undesired directions if the lance were dropped.
More recently, there have been two innovations to this type of cleaning lance. In a first innovation, a pair of triggers are provided on the lance. The two trigger lances require the operator to have the lance firmly held in two hands, with both triggers closed. If either trigger is opened, then the valve opens. An example prior two trigger lance is shown in U.S. Pat. No. 5,904,297, which is owned by the assignee of the present invention.
One other recent innovation is the replacement of the mechanical connection with electric trigger switches. A control monitors whether the trigger switches are closed, and opens the dump valve should a trigger switch be released. The electronics necessary for the operation of such a valve are known in this art.
One problem with the above-discussed two trigger devices is that users have sometimes tried to circumvent the “double” trigger safety function. In the past, users have been known to tape one of the triggers closed such that the lance need not be held in both hands firmly. This obviously defeats the purpose of the two-switch safety device.
In the disclosed embodiment of this invention, a control for a lance monitors whether the two triggers in a two-switch safety circuit are being operated by an operator, or whether one of them appears to be blocked closed. If one of the two switches appears to be blocked closed, then the control will not allow the dump valve to close until the switch appears to again be functioning properly.
In a disclosed embodiment of this invention, the two triggers are electric switches. A control monitors the opening and closing of the switches. If one of the two switches is open, and the other is not, the dump valve is opened. This is consistent with the prior art, wherein the dump valve is opened whenever one of the two switches is released. However, and contrary to the prior art, the dump valve is not allowed to close until both triggers have been opened.
Consider a situation such as has occurred in the prior art where one of the two switches is taped closed. When the other switch is released, the dump valve is opened. The control will not close the dump valve until the taped closed switch is also released, or opened. If an operator has taped one of the two switches closed, the control will not allow the dump valve to close until that taped closed switch has opened.
In a preferred embodiment, the switches are electric switches and the dump valve is electrically controlled. A controller is preferably mounted remote from the lance, and appropriate circuitry communicates the switches to the controller, and the controller back to the dump valve.
Various sequences of operation the switches may also be required in order to close the dump valve.
These and other features of the present invention may be best understood from the following specification and drawings, the following of which is a brief description.
As shown in
It should be understood that the water is typically delivered at extremely high pressures which could be somewhat dangerous if the water were directed against undesired surfaces. Thus, the switches 30 and 32 not only allow the operator to stop the flow of high pressure water, but also provide a safety function, such as if the lance were dropped.
As mentioned above, it has been the case in certain circumstances that one of the two switches 30 or 32 have been taped or otherwise held closed by an operator who would like to hold the lance with a single hand. The present invention addresses this concern.
As is shown in
The control 42 preferably operates according to a flow chart such as shown in FIG. 3. As shown, at step 1, the valve 34 is held closed with water being directed toward the nozzle. However, should one or both of the two switches be opened, then the valve is driven to the dump position. Once in the dump position, the control will only move the valve to the closed or operative position if both trigger switches have been held open and then closed. If only one has been opened, then the dump valve will not be moved to its operative position.
In this way, should an operator tape one of the two switches 30 or 32 closed, the system will not operate to direct high pressure fluid until the tape is removed. While the term “taped” has been utilized, any other way of trying to deactivate one of the two safety switches, would come within the scope of this invention. Moreover, various sequences of control of the two switches may be incorporated into the control to provide further levels of safety.
Generally, should an operator release one of the two triggers, the operator would know that the other trigger must also be released to then allow the dump valve to move back to the operative position once both figures are closed. Various sequences of closing of the two triggers could be required to provide further control over the closing of the valve.
While a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. Thus, the following claims should be studied to determine the true scope and content of this invention.
Number | Name | Date | Kind |
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2138279 | Kneisley | Nov 1938 | A |
4538142 | Hamilton et al. | Aug 1985 | A |
4678892 | Finger et al. | Jul 1987 | A |
4716401 | Wohlford et al. | Dec 1987 | A |
5069391 | Seasholtz | Dec 1991 | A |
5904297 | Kendrick et al. | May 1999 | A |
5938472 | Yuen et al. | Aug 1999 | A |
Number | Date | Country | |
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20040144855 A1 | Jul 2004 | US |