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AUTOMATED SELF-CLEANING STRAINERS

We offer several designs of automated self-cleaning strainers and filtration systems, following is an overview of standard designs with key aspects for selection.

 

INEXPENSIVE SELF-CLEANING FLUSHING STRAINERS

Flushing strainers are an inexpensive design, performing similar to flushing of a toilet, material that has accumulated within the strainer basket will tend to "flush" out the drain when the drain valve is opened.  (The drain valve, supplied by others, can be manual or automated)  The finest mesh available is 200 mesh (≅50 microns) and material of construction carbon steel or 316SS.  Some fluid is purged along with the particulates, the volume dependent upon the fluid characteristics, system pressure and duration of the cleaning cycle.  Flow does not reverse through the element to dislodge embedded particles.  Best for a low percentage of particles that tend to be hard and heavy.

 

BACKWASHING STRAINERS FOR WATER APPLICATIONS (particle retention as fine as 150 microns) 

 

With a proven design that is decades old, backwashing strainers are the most common style of automated designs. Fluid enters into the strainer body and must travel upwards through a stainless steel element.  Heavy particulate immediately sink to the bottom, smaller particulate are pressed to the element surface, gradually reducing the differential pressure across the element.  Once the differential pressure is sufficient (a settable variable), the drain valve opens.  Within the strainer the drain valve is connected to a nozzle arm (it looks like a wide vacuum cleaner nozzle) and the assembly slowly rotates.  Because the system pressure is greater than atmospheric pressure, the flow reverses wherever the cleaning nozzle rotates past, effectively using a portion of the filtered water to clean the element.  The duration of cleaning is typically only a few minutes and the clean fluid drained is about 5% of the flow.  Once the pipeline size exceeds 8", the cost for a manually operated duplex strainer is typically more than a comparable sized backwashing strainer. 

 

These are almost exclusively designed for water applications due to the volume of fluid used for cleaning the element and they are designed for particle sizes as small as 150 microns (100 mesh) at concentrations ≤ 200 PPM.  Applications that require finer particle retention use a variation referred to as a tubular backwashing filter.

 

BACKWASHING FILTERS (particle retention as fine as 3 microns)

Backwashing filters operate on a similar principle to the backwashing strainers above, essentially isolating a portion of the total filter area and temporarily reversing the flow across the element.  Our backwashing filters consist of multiple filter stations connected to common inlet, outlet and drain manifolds.  During the backwashing stage each filter station is is isolated in series, closing the inlet and opening the drain, thus reversing the flow across the element due to the system backpressure. 

Tubular filter flow path during filtrationTubular filter flow path during backwashing

Since only one filter station is in backwash mode at a time, a properly sized system will result in negligible pressure drop during the backwashing process. 

 

Other advantages of this system design include an option to backwash from an external source.

 

The backwashing frequency is programmable by time or differential pressure and the valves can be either electrically or air actuated. 

 

MECHANICALLY CLEANED STRAINERS AND FILTERS (particle retention as fine as 15 microns to ¼")

Mechanically cleaned strainers and filters are used for both water and non-water applications to minimize lost product during the cleaning cycle. This type of automatic strainer is also used for viscous and other "difficult to handle fluids".  A specially designed internal cleaning disc physically pushes the particles which accumulate onto the screen surface into a purge chamber.  The material within the purge chamber is pushed out based upon the system pressure typically within 1 second, resulting with a concentered volume of unwanted particles, very little product waste and minimal process fluid loss.

 

The actuation of the cleaning stroke and purge requires compressed air and the frequency is typically controlled by timer or differential pressure. 

 

Your fluid type and application description dictates which design would be the more cost effective approach. Why not fill out our inquiry form for a no obligation, detailed proposal?