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Q. What is the difference between a Filter and a Strainer?
A. A strainer is used to "strain" out large particles whereas a Filter is used to "filter" the fine particles. There is not a clear-cut, internationally recognised, size of particle removal at which a strainer becomes a filter or vice versa.
Some types of equipment clearly fall into one category or the other i.e. T or bathtub units are always called strainers (normally 0.5mm and larger particle removal), whereas units incorporating disposable cartridge elements are always called filters (normally 20 micron and smaller particle removal).
Most of the equipment supplied by Plenty Filters can be classed as either a filter or strainer depending on the element fitted. For example a Simplex type S can be fitted with a coarse 2mm diameter perforated basket making it a strainer, or a disposable cartridge giving 2 micron particle removal making it a filter. The best solution is not to worry about the name, instead make sure that the filter or strainer will remove the particle size you require.
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Q. What does the mesh number mean and is it the same as micron?
A. Mesh numbers and microns are two very different things. A micron is a unit of measurement and 1 micron = 1/1000th millimetre. Micron is used to indicate the particle size to be removed, or minimum particle size that the filter will stop. Therefore the smaller the micron number the smaller the particles that will be removed.
With filters and strainers that have an element manufactured from woven wires then a mesh number is used to indicate the number of wires. The normal weave consists of vertical and horizontal wires woven in a simple over, under, over, under. pattern. The mesh number is the number of wires in one inch vertically and one inch horizontally. A 20 mesh therefore has 20 vertical wires per inch and 20 horizontal wires per inch. The bigger the mesh number, the more wires that are used per inch and the smaller the particle size (exactly the same principal as denier numbers used to grade tights and stockings!)
As a mesh number increases the micron size will decrease.
Please note that various wire diameters can be used and a 20 mesh with small diameter wire will have a larger hole and micron rating than a 20 mesh with a larger diameter wire. This is because the actual hole through which the liquid passes will be a square where each side has a dimension of one twentieth of 1" minus 20 x wire diameter. There are also different "standards" used in USA and Europe so the safest way to ensure you remove the particle size you desire is to state the micron rating and not the mesh number.
For your information the mesh numbers and micron ratings used as standard by Plenty are as follows:-
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Plenty, UK
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Plenty, U.S.A.
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| Mesh No. |
Micron Rating |
Mesh No. |
Micron Rating |
| 20 |
920 |
20 |
864 |
| 30 |
570 |
30 |
508 |
| 40 |
410 |
40 |
381 |
| 60 |
260 |
60 |
229 |
| 80 |
178 |
80 |
178 |
| 100 |
142 |
100 |
152 |
| 120 |
122 |
120 |
117 |
| 150 |
109 |
150* |
104 |
| 180 |
91 |
180 |
84 |
| 300 |
45 |
300 |
46 |
* Not a stock part, available to order.
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Q. What is a Duplex Filter?
A. This is a basket filter (or strainer) which can be used for continuous service without interruption to the flow even during cleaning of the basket. Within a single Duplex filter there are two basket chambers each rated to handle 100% of the liquid flow plus an integral valve mechanism that enables the flow to be diverted through either chamber. The integral valve mechanism is safer than an operating / standby piping layout incorporating separate valves in which the flow can easily be interrupted if the valves are operated in the wrong sequence.
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Q. What is the difference between a "Self Cleaner" and a "Backflusher"
A. A Backflusher relies on reversing flow through the screen to flush collected debris to waste. This can take place whilst the unit is "on-line" but some of the process flow is flushed to waste during the backwash cycle. For this reason backflushers are generally only used on water systems where the process flow (water) has a low value and can easily be disposed of.
A self cleaner relies on a mechanical scraping action to remove the debris collected on the screen. The accumulated debris collects in the body and can then be periodically flushed to waste and the whole process can be performed whilst the unit remains "on-line". As a self cleaner only discharges a small amount of process flow during the flushing to waste the unit can be used on process flows with a high commercial value such as oil, chemical, paint etc. In addition, due to the low loss of process flow, the self cleaner also reduces environmental and waste disposal problems.
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