Filters minimise maintenance costs

In an on-going drive to reduce the maintenance costs of their filters, Rosedale Products Europe have developed a backwashing bag type fluid filter

In an on-going drive to reduce the maintenance costs of their filters, Rosedale Products Europe have developed a backwashing bag type fluid filter in which pressurised air can be released into the inside of the filter bag in the opposite direction to the normal filtering flow.

Accumulated particulate contaminant on the surface of the bag is dislodged and transported to a safe location.

The units can be cycled through many backwashes before any further servicing is required.

Thus filter bags which are normally disposed of when full, can be re-used many times.

The actual number of cycles depends on several factors.

For instance felt media will have a shorter life than monofilament nylon.

Contamination type and size also have an effect on bag life and the period between backwashes.

As well as reducing the cost of media disposal and replacement, backwashing filters have other benefits: Less downtime means increased productivity, labour costs are slashed and operator exposure to potentially hazardous substances is substantially reduced.

In a standard Rosedale bag filter the fluid flow is from inside the bag outwards so that dirt accumulates on the inside of the bag; an external perforated support cylinder retains the bag against the flow.

In a backwashing filter however the bag is positioned between internal and external support cylinders.

These retain the bag against the filtering flow which is from outside the bag inwards and the backwashing air flow which is passed through the bag from the inside to the outside.

Two gauges fitted to the housing show the pressure differential between the dirty and clean sides of the unit.

An increasing pressure differential indicates the level of contamination build-up on the outside of the bag.

When a pre-determined pressure differential is reached, filtering is suspended by closing valves in the inlet and outlet pipework to isolate the normal filtering system.

Another valve is opened to the backwashing pipework, then a button is depressed allowing factory air to the centre of the bag to shock the backwashing system.

It loosens the accumulated contaminant which is flushed away for disposal via the backwashing valve.

The procedure takes about 30 seconds after which the valves are returned to their normal positions and filtering is resumed.

Rosedale Backwashing Filters use standard 762mm long filter bags manufactured from any of the standard media types.

Carbon steel or 316 stainless steel housings rated at 10 bar have seals and valves manufactured from a variety of materials to suit the application.

Pipe sizes are 2, 3 or 4 inches with either BSPF female threaded connections or ANSI flanges.

The foregoing description refers to the use of bag filters but backwashing is equally suitable for coarse filtration systems using stainless steel meshes rather than filter bags.

These filters will operate for long periods without the need to open the housing for cleaning.

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