Tidal ^® Series 5
Level control for dry bulk materials

How the Tidal Operates

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.

Tidal Unit Control Range

			Unit Assy. Ref. No. with
Diaphragm Type	Retained By	Micro Switch Type	One Switch	Two Switch
Nitrile Rubber	Polypropylene Ring	Standard	042/0172	042/0178
Silicone Rubber	Polypropylene Ring	Standard	042/0175	042/0181
Silicone Rubber	Mild Steel Ring	Standard	042/0174	042/0180
Polyurethane	Mild Steel Ring	Standard	042/0173	042/0179
Silicone Rubber	Mild Steel Ring	Heat Resistant	042/0182	-

Specifications

The housing

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 prevent 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.

Diaphragms

• Nitrile Rubber Diaphragms
  For general use within the range of -20ºC to + 100ºC (intermittent +130ºC). Resistant to mineral and vegetable oils and acids; odourless, tasteless and suitable therefore for use with foodstuffs.
• Silicone Rubber Diaphragms
  Suitable for use within the range -70ºC to +205ºC (intermittent +250ºC). Resistant to animal, vegetable and heavy lubricating oils.
• Polyurethane Diaphragms
  Abrasion resistant material with dry temperature range -40ºC to +80ºC (intermittent +100ºC). For moist environments the temperature should not exceed 50ºC Resistant to petrol and lubricating oils, 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.

The Switch

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 normally open circuit. Release of the diaphragm permits 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 -40ºC to +85ºC. A heat resistant switch up to +250ºC 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 are employed to obtain any additional contacts.

		Loads (amps)
Switch Type	Volts	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 5 1.25 0.75 0.50 0.255	10 5 1.25 0.30 0.05 0.03
Heat Resisting	up to 480 AC	1	1
	up to 75 DC 125 DC 250 DC	1 0.5 0.25	1

Typical Installation Arrangements

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.

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”.

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 also low level units are subjected to rapid wear by the frequent sliding of abrasive materials across their diaphragms

Planning in Detail

Typical Wiring Diagrams