| 1 | Diaphragm |
| 2 | Screws |
| 3 | Retaining Ring |
| 4 | Actuator |
| 5 | Adjusting Spring |
| 6 | Microswitch |
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The Stock Redler Tidal Control Unit detects the level of material in a hopper or bunker. It has a flexible diaphragm covering one or two microswitches. When the Tidal diaphragm is covered with material, the pressure exerted on it operates the microswitches. As the material falls away from the diaphragm, it is free to return to its original position and the switches are released. These units can be used in high-level or low-level situations to regulate the amount of material in the hopper.
Another application of the Tidal is to monitor the discharge chute from a process. During normal operation, the Tidal on the far side of the chute is not covered. When the chute becomes blocked, the Tidal is covered, and the control system shuts down the feed to the chute.
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Diaphragm Type
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Retained By
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Micro Switch Type
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Unit Assy. Ref. No. with
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One Switch
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Two Switches
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Nitrile rubber
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Polypropylene ring
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Standard
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042/0172
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042/0178
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Silicone rubber
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Polypropylene ring
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Standard
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042/0175
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042/0181
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Silicone rubber
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Mild Steel ring
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Standard
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042/0174
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042/0180
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Polyurethane
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Mild Steel ring
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Standard
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042/0173
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042/0179
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Silicone rubber
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Mild Steel ring
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Heat Resistant
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The Tidal Control Unit consists of a diaphragm whose movements are transmitted by a lever to an electrical switch which is enclosed in a housing of which the diaphragm forms one side. Bolted to the side of the chute, hopper or bunker, the movement of the diaphragm caused by accumulation of material, is used to actuate the switch to stop or start machinery or operate signal lamps and hooters.
Units are readily available for working in conjunction with most powdered or granular materials up to 40-50mm (1½” – 2”) in size with a minimum loose bulk density of approximately 300kg/m3 (20lb/ft3).
The characteristics of the material should be such that it will flow sufficiently well to exert a side pressure against the diaphragm without any tendency to cling or bind together and that it will fall freely away without undue sticking or caking over the diaphragm as the level of the material drops in the bin.
The largest lumps of material should not be so large as to be likely to bridge across the diaphragm. The customer should satisfy himself that his particular material fulfils the above requirements but should there be any doubt we would be pleased to supply a unit on ‘sale or return’ for test purposes.
The diaphragm reacts to air pressure and we do not recommend the use of these units for pneumatically fed installations unless a customer is satisfied that he can satisfactorily balance the pressure both sides of the diaphragm.
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This method is satisfactory with a low head of material, but the feed to the hopper should be arranged so that lumps cannot drop on to the Tidal Control diaphragm. |
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When considerable pressure is expected the unit may be mounted vertically. The shelf above the unit can be hooded to prevent accumulation of “dead material”. |
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The decision to use the Tidal Control Unit for low level indication must take into account the fact that low level units are covered for much of the time by material. Some materials have the ability to agglomerate and interfere with the free movement of the diaphragms, and low level units are subjected to rapid wear by the frequent sliding of abrasive materials across their diaphragms. |
The housing is of aluminium to BS 1490:1988, the body to LM25 and the cover to LM6, both of which are gravity die castings having a high resistance to corrosion, painted a silver grey hammer finish. An epoxy painted version for additional protection against corrosion is also available to order.
One conduit entry is provided tapped M20 x 1.5. The breather hole adjacent to the conduit entry is tapped 1/8” BSP enabling client to fit a pipe between the housing and the bin, via a manometer or other form of dust trap, to balance any differential pressure such as with pneumatically fed installations. A filter is usually fitted in the breather hole to proven the ingress of dust from a normal atmosphere. This should be removed when making pipe connections. A gasket and four M10 x 16 hex. Set screws are supplied for mounting.
NITRILE RUBBER DIAPHRAGM
For general use within the range of -20°C to +100°C (intermittent + 130°C). Resistant to mineral and vegetable oils and acids, odourless and tasteless and suitable therefore for use with foodstuffs.
SILICONE RUBBER DIAPHRAGMS
Suitable for use within the range -70°C to +205°C (intermittent +250°C). Resistant to animal, vegetable and heavy lubricating oils.
POLYURETHANE DIAPHRAGM
Abrasion resistant material with a dry temperature range -40°C to +80°C (intermittent 100°C). For moist environments the temperature should not exceed 50°C. Resistant to petrol and lubricating oils and grease, most solvents and weak acids.
Diaphragms are normally secured to the face of the housing by a polypropylene ring but mild steel rings are also used with silicone rubber and polyurethane diaphragms.
Both the standard switch and the heat resisting switch are single pole changeover micro switches. Each has three contacts, two fixed and one movable which alternately contacts one or other of the fixed contacts. One fixed contact is normally closed, the other normally open. Pressure on the Tidal Control diaphragm opens the normally closed circuit and closes the switch automatically to return to its original position. The appropriate connections are marked on the switch.
The standard switch is suitable for the temperature range of -40°C to +85°C. A heat resistant switch up to +250°C is also available. Although units can be supplied to order fitted with two standard micro switches it is difficult to ensure simultaneous operation on both switches and it is therefore recommended that relays be employed to obtain any additional contacts. The unit is not certified as flameproof, the Tidal Control may be used in these areas providing it is connected to an approved intrinsically safe circuit.
The electrical ratings are as follows:
| Switch Type | Volts | Loads (amps) | |
| Resistive | Inductive | ||
| Standard | up to 250 AC 380 AC 480 AC |
15 15 15 |
15 5 4 |
| up to 15 DC 30 DC 50 DC 75 DC 125 DC 250 DC |
15 |
10 5 1.25 0.30 0.05 0.03 |
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| Heat Resisting | up to 480 AC | 1 | 1 |
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up to 75 DC |
1 0.5 0.25 |
1 |
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The Tidal Control Unit should be mounted either on a vertical face or at an inclination such that accumulating material will exert sufficient pressure to depress the diaphragm and receding material will freely gravitate clear. Units mounted on an inclined face are suitable with a limited head of material but the feed should be such that the material does not drop directly on to the diaphragm. The gasket provided should be fitted between the Tidal Control Unit and the mounting face.
A 6mm (¼”) thick mild steel mounting plate 260mm (10¼”) square for welding to the mounting surface is available for use where the wall is too thin for drilling and tapping for direct mounting and there are no facilities for stud welding.
The series 5 unit may be used to replace earlier types but it should be turned through 45º to pick up on four of the original fixing bolts and, therefore, a minor modification to the conduit connection will be required.
Periodic inspection should be carried out, particularly of the diaphragm, which should be replaced if wear or loss of flexibility is apparent. The diaphragm is secured by a ring screwed to the face of the housing, one hole of which is offset to ensure that the position of the ring remains constant and when refitting a diaphragm it is therefore important to ensure that all holes match before inserting the screws.
A coil spring maintains a constant pressure against the lever operating the switch and frees the switch actuator lever when the depressed diaphragm is relieved of pressure. The pressure of the spring is variable by means of a nut. When the Tidal Control has been installed the nut may be adjusted, if necessary, so that the switch or switches operate when the diaphragm is between a half and three-quarters covered with material.
Carton size approx: 257x275x115mm (10¾”x10¾“x4½”)
Nett weight approx: 2.1kg. (4½lb.)
Gross weight approx: 2.6kg. (5¾lb.)
