The present invention relates to a pressure jet cleaning appliance with a pressure pump driven by a driving means from whose pressure pipe a bypass pipe, which, when the pressure pipe is closed, is opened by means of a closing valve provided with a closing element, leads to the suction pipe of the pressure pump and having a control element that is connected to a governor of the driving means.
In non-stationary operating pressure jet cleaning appliances, an electromotor or an internal combustion engine is frequently employed as driving means of the pressure pump that is operated at a constant rotational speed. In the case of the electromotor, the rotational speed control is effected independently of the load by means of the fixed number of poles and the constant mains frequence and, in the case of the internal combustion engine, by means of a rotational speed-dependent throttle valve position. In such a case the control of the system is effected in that, with the opened spray gun, the driving means drives the pressure pump with the power that is necessary for the operation of the pressure jet cleaning appliance. When the spray gun is then closed with the aid of the normally provided control handle, a bypass closing valve enters into action in such a way that, when the pressure pipe is closed by the spray gun, a bypass pipe to the suction pipe opens so that the pressure pump then delivers the cleaning fluid into the circulation. The power of the pressure pump that is necessary in this bypass operation is considerably less than the power required in the normal spraying, squirting or cleaning operation.
In order to reduce the noise development and the wear during the operating intervals (bypass operation), a control is expediently effected in that, when the pressure pipe is closed, the driving means is regulated down to a rotational speed that is lower than the nominal operating speed.
For this, in a known high-pressure jet cleaning appliance, a pressure sensor is provided in the pressure pipe which detects the pressures which occur inside the pressure pipe, in particular the lowering of the pressure which occurs after the closing of the pressure pipe and the opening of the bypass valve connected therewith, and the increase in the fluid pressure which occurs in the pressure pipe following the reopening of the pressure pipe and reduces the rotational speed of an internal combustion engine provided as driving means as soon as the pressure in the pressure pipe, due to the opening of the bypass valve, drops below a certain value and, when a certain pressure value is exceeded, once more adjusts the throttle control rod of the internal combustion engine to an increase in the rotational speed (DE 39 02 252 C1).
However, this method of regulation is subject to various disadvantages. For it has to be stated that such a control system operates according to quite specific pressure changes which arise in the pressure pipe under quite specific directions subsequent to the opening or closing of the bypass valve, said changes being then utilized for the control. This means that the control is merely able to lag timewise behind the pressure conditions occurring, that is to say, the control becomes only effective when a rise in pressure or a drop in the pressure has taken place.
Furthermore, in pressure jet cleaning appliances there arises the problem that an operation of the pressure jet cleaner is only possible at one pressure, viz. the maximum pressure, independently of the circumstance whether this pressure is actually required. That is why it is desirable to adapt the pressure of the squirted-out cleaning medium as well as the driving power needed herefor to the case of application. With the DE 39 22 956 A1, a high-pressure jet cleaning device has already been proposed which comprises a high-pressure pump, a pressure pipe leading from the latter to a closable outlet, a bypass pipe leading from the same to the induction side of the pump and a closing valve that closes the bypass pipe. The device makes an automatic pressure discontinuation of the pump possible when closing the outlet, is constructed in such a way that, upstream of the outlet and downstream of the branching of the bypass pipe, a flow controller is provided which closes the closing valve of the bypass pipe when the outlet is closed. In this case the closing valve is constructed in the form of a closing valve and provision has been made for an adjustable stop, with the aid of which the closing motion of the closing valve can be limited. However, with such a set-up, only the volume flow is regulated.
This invention is based upon the technical problem of constructing, in a pressure jet cleaning appliance of the type stated in the beginning, a control in such a way that the same is independent of pressure changes that occur due to the closing or opening of the closing valve and, more particularly, prior to the occurrence of these pressure changes, adjusts the rotational speed of the driving means.