GB2120762A - Electrode boiler - Google Patents

Abstract

A lifting mechanism is provided for electrode hot water boilers which comprises a lifting screw 18 mounted for rotation and carrying a lifting plate 16 to which are attached electrode insulators 14, the screw 18 having at its upper and lower extremities 22, 24 plain portions which cannot transmit drive to the lifting plate 16. Helical springs 28, 30 are also provided at each extremity to urge the plate 16 back towards the threaded portion of the screw 18 so that reengagement with the lifting plate will be facilitated when the screw 18 is reversed in direction of rotation. Movement of the insulator 14 beyond its normal upper and lower limits of operation is thereby prevented. <IMAGE>

Description

SPECIFICATION Electrode hot water boiler This invention relates to improvements in electrode hot water boilers, and in particular to the improvements in the control mechanism therefor.

Electrode hot water boilers produce hot water from electricity directly by the immersion of electrodes in the water. In normal operation the boilers are filled with water and the rate of hot water production is controlled by raising or lowering an insulating shield between the live and neutral electrodes thereby adjusting the effective electrode operating area. One common form of electrode hot water boiler has electrodes projecting from the basr of the boiler upwardly. The electrodes are generally in the form of cast iron alloy rods, and above each electrode suspended from a suitable mounting plate is a cylindrical insulator of porcelain, glass or plastics material.The supporting plate is mounted on a thread mechanism turned by an electric motor thereby alowing the cylindrical insulators to be moved up and down into and out of register with their associated electrodes thereby controlling the power consumption of the boiler.

In order of prevent damage to the lifting and lowering mechanism or to the insulators, the motor operating the lifting mechanism is usually fitted with limit switches. However, it often frequently happens, after disassembling the mechanism for maintenance, or during fault finding checks, that the motor is connected for rotation in the wrong sense thereby negativing the effect of the limit switches: or manual over-ride of the limit switches is achieved during test procedures by making manual connections within the control panel.

In either of these cases, considerable damage can be done to the insulators and/or the lifting mechanism.

The invention seeks to provide an improved form of lifting mechanism for the control of electrode hot water boilers in which the above disadvantages are reduced or eliminated.

According to the present invention there is provided a lifting mechanism for electrode hot water boilers which comprises a lifting screw mounted for rotation and carrying a lifting plate to which are attached electrode insulators, the screw having at its upper and lower extremeties a plain portion not capable of transmitting drive to the plate, and means at each extremity for biasing the plate towards the threaded portion of the screw.

By the mechanism of the invention, movement of the insulator carrying plate beyond its normal upper and lower limits of operation is prevented in that the screw is so constructed that it can not transmit drive beyond those regions. Thus operation of the device overriding the limit switches, or if the motor is connected to rotate in the opposite sense, can not result in damage to the mechanism or to the insulator.

Means for biasing the plate back towards the threaded section of the screw, for example mechanical springs, are also provided so that if the plate is inadvertently taken into one of the plain areas reversal of rotation of the screw will cause it to re-engage the threaded portion and operate normally once again.

In a preferred embodiment of the invention a control circuit is additionally provided to shut off the drive to the thread operating motor if the latter is operated for a pre-set period longer than its traverse time. Thus, if the motor, in normal operation, required four minutes to traverse from fully in register to fully out of register then a five minute delay relay could be employed to shut off the motor should it continuously operate for more than five minutes. This prevents continuous operation of the motor in event of incorrect connection.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevational view partly in section of an electrode hot water boiler having a control mechanism constructed in accordance with the invention; and Figure 2 is a circuit diagram of a suitable control circuit.

Referring to the drawings, an electrode hot water boiler 10 is illustrated having a series of rod like electrodes 1 2 of cast iron alloy projecting upwardly from its base plate. Each electrode has an associated insulating cover 14 mounted from a lifting plate 1 6 which is in turn mounted on a rotating screw 18. The latter is driven by means of an electric motor 20 as is normal in boilers of this type. Rotation of the screw 1 8 lifts or lowers the lifting plate and the insulators 14 into and out of register with their respective electrodes 1 2.

The electrodes 1 2 are the "live" electrodes and each has an associated cylindrical "neutral" electrode 20. The insulator 14 moves between the two thereby controlling their effective area and hence the power consumption of the boiler. In the modified mechanism according to the invention, the upper and lower extremities 22, 24 of the screw 1 8 have no thread and can not therefore transmit drive to the internally threaded nut portion 26 of the plate 1 6. Helical springs 28, 30 are provided at each extremity to urge the plate 16 back towards the threaded portion of the screw 18 so that re-engagement of the nut 26 will be facilitated when the screw 18 is reversed in direction of rotation.Additional helical springs 32 may be provided on each of the guide rods 34 which pass through bushes 36 close to the periphery of the plate 1 6.

In addition to the mechanism described above a motor over-run prevention circuit may be provided as illustrated in Fig. 2. In addition to the largely conventional control circuit for the boiler the relay contacts 38 of a latching relay 42 may be interposed in the motor control circuit. The latching relay 42 is actuated by means of a time delay relay 40 actuated by additional contacts 44 and 46 on the "raise" shield motor starter 48 and the "lower" shield motor starter coil 50 respectively.

In operation, supposing the motor is switched to the "raised" mode the contact 46 is closed thus actuating the time delay relay 40. The latter is set with a time delay somewhat longer than the time taken for a full traverse of the plate 16 from one extremity to the other of the screw 1 8. For example, should the traverse take four to five minutes, the time delay relay 40 may be set to a time delay of six minutes. Thus, should the contact 46 remain closed for the pre-set time the relay 40 will trip the latching relay 42 thereby permanently disconnecting the contact 38 and preventing further actuation of the lifting motor. Similarly, on actuation of the "lower" command 50 the contact 44 is closed also sending a signal to the time delay relay 40 which, if it exceeds the pre-set time, will likewise cause the latching relay 42 to disconnect its supply to the motor. In this way overrunning of the motor caused by incorrect connection of the limit switches, incorrect connection of the sense of sense of rotation of the motor, or manual over-ride on the control board, is prevented.

Thus, the mechanism of the invention, and the control circuit of the invention serve to prevent damage to the electrode insulators, the lifting mechanism, and the lifting motor.

Claims (4)

1. A lifting mechanism for electrode hot water boilers which comprises a lifting screw mounted for rotation and carrying a lifting plate to which are attached electrode insulators, the screw having at its upper and lower extremities a plain portion not capable of transmitting drive to the plate, and means at each extremity of biassing the plate towards the threaded portion of the screw.

2. A mechanism as claimed in claim 1 in which means for biassing the plate back towards the threaded portion of the screw comprise mechanical springs.

3. A mechanism as claimed in any one of claims 1 or 2 in which a control circuit is additionally provided to shut off a drive to the thread operating motor if the latter is operated for a preset period longer than its traverse time.

4. A lifting mechanism for an electrode hot water boiler substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.