Patent GB-872662-A (GB)
Title: A monitoring means for fluid level indicators
IPC: G01F23/60
Filed: 1958-10-20
Abstract: 872,662. Indicating liquid-levels. MARSHALL SONS & CO. Ltd., and HOWE, C. A. Oct. 16, 1959 [Oct. 20, 1958], No. 33362/58. Class 123(1) In a monitoring device for periodically checking a float 20 in a float chamber 2 the latter is connected to a boiler shell 1 by a pipe 3 and a three-way valve cock 5. The latter is rotatable to connect any one of three branches 6, 7, 8 with either of the other two and is slowly rotatable by a non-reversible motor 14 acting through a reduction gear and drive unit 16 which reverses the direction of the valve cock 5 at the end of every 180 degrees of rotation. The unit 16 drives a camshaft 18 which controls contacts 18a, 18c, 18d, 18e in an electrical control circuit Fig. 4 a time switch 17 closing a contact 17a, approximately every four hours, to connect the motor 14 between phase and neutral lines 23, 24 so that the valve cock 5 rotates slowly in the direction of the arrow C and the initial rotation of the camshaft 18 closes contacts 18e, 18a, the latter maintaining the motor 14 energised when the time switch reopens the contact 17a, and opens a contact 18d. Should the float 20 be functioning properly and follow the drop of the level of the liquid in the chamber 2 when the valve cock 5 approaches the draining position, Fig. 2, contacts 22a of a switch 22 are opened so that a relay R 1  is de-energised contacts R1b of which are opened to interrupt the supply to a relay R 2  and open contacts R2a, R2b the latter de-energising a relay R4 which operates oilfiring shut-down mechanisms, not shown, of the boiler. The opening of contacts R1c of the relay R1 ensures that a float-warning circuit, including a de-energised holding relay R 3  the contact 18e and a contact R2c of the relay R 2  which at this time are closed, is not established and a warning light 29 is not operated. When the float 20 has dropped to the danger level B, Fig. 1, contacts 22b of the switch 22 are closed to supply energy to an alarm device incorporating an audible unit 27 and a warning lamp 28. When the valve cock 5 reaches the fully drained position Fig. 2 the contact 18c opens so that if there is leakage into the chamber 2 when the valve cock 5 reaches the position in which water is drained from the boiler 1 to flush the drain pipe 10, Fig. 3, the relay R 2  cannot be energised should the contacts 22a be closed by the float rising with the leakage water. The valve cock 5 now commences to rotate in the opposite direction the contact 18e being closed as connection between the branches 6, 7 is re-established and the float 20 rises to close the contacts 22a, re-energise the relay R 1  and stop the alarm device 26 to indicate that the alarm was the result of a monitoring procedure and not due to a fall of the water in the boiler to the danger level shown in Fig. 1. As the valve cock 5 is returned to its original position shown in Fig. 1 the contacts 18d close and the contacts 18a, 18c open. By depressing a manual reset button 30 the boiler attendant can re-energise the relay R 2  the contacts R2c being opened and the contacts R2a, R2b being closed. Assuming, e.g. that due to sludge, the float 20 is unable to fall as the valve cock 5 approaches the position in which the float chamber 2 is connected to the drain 10 the switch contacts 22a remain closed and the relay R 1  remains energised. When the valve cock 5 reaches the position shown in Fig. 2 contacts 18c open to cut off the supply to the relays R 2 , R 1 , the latter initiating shutdown of the oil firing mechanism of the boiler and the former relay closing contacts R2c to complete the float warning circuit through the closed contacts 18e and R1c the contacts R3a of the holding relay R3 also being closed so that the contacts R3a remain held-in after the valve cock 5 has been returned to rest in the position shown in Fig. 1 and the motor 14 has been stopped. When the float failure has been rectified the reset button 30 is depressed to re-energise the relays R 1 , R 2 , R 3  so that the lamp 29 is extinguished and the holding relay R 3  is de-energised the system then being restored to the original condition as shown in Fig. 4 with the oil firing shut-down control inoperative again. If desired the relay R 3  may be provided with a further contact, not shown, which is open when the relay R 3  is energised and which is in series with the press button 30 so that the re-energisation of the relays R 1 , R 2 , R 3  cannot take place even if the press-button has been depressed until the failure of the float to descend has been rectified. The drive unit 16 is preferably connected to the valve cock 5 through a manually operable clutch 19 which is normally spring-loaded into its engaged position and the valve cock 5 is provided with a handle 12 for manual operation. The closing of a press-button 25 commences a monitoring process in addition to that initiated by the time switch. If desired a further contact, not shown, actuated by the camshaft 18 can be arranged to disconnect the alarm device 26 during monitoring and to connect an additional alarm device. Also the time switch 17 may be provided with an extra contact to operate an electric locking device for the clutch 19 to prevent manual disengagement of the clutch, immediately prior to the beginning of a monitoring process. The electric motor may be replaced by a steam or a hydraulic motor the control of the working fluid of which may be effected by an electrical control actuated by the time switch 17. Alternatively the latter may control a mechanical servo-mechanism controlling the working fluid of the motor. The valve cock 5 may be replaced by one or more solenoid operated valves.