Frequently Asked Questions

Engineers and operators throughout the municipal, industrial and irrigation markets use a variety of terms to specify or describe Forsta’s self-cleaning filters.  The language in a spec may be as simple as “water filter.” The following detailed terms have also been used in official spec language:

Automatic Self-Cleaning Filter, Automatic Water Filter, Self-Cleaning Strainer, Service Water Strainer, Automatic Suction Scanner, Screen Filter, Self-Cleaning Screen Filter, Inline Screen Filter, Automatic Sediment Removal Filter, Motor-Operated Strainer, Backwashable Screen Filters, Horizontal Self-Cleaning Filters, Vertical Self-Cleaning Filters and more.

Submit a spec for review to if you have questions about whether or not Forsta’s equipment meets project requirements.

Self-Cleaning Filter Performance Checklist

A. Refer to the numbered diagram above and corresponding answers below to understand the 3 checkpoints for success.

1) Confirm screen selection is appropriate for source water quality.

Click here or scroll down to learn more about screen selection based on water source.

2) Check for sufficient inlet pressure during backwash.

All Forsta self-cleaning water filters utilize system pressure to drive the internal cleaning mechanism. A minimum of 35psi (15psi for Low Pressure models) is required for proper backwash performance. This should take into account the flow and head loss expelled through the flush valve as well as the system flow.

3) Minimize back pressure on the flush line.

Since backwash is based on system pressure, it is critical that the flush piping be designed in such a way as to minimize back-pressure. Ideally the flush piping will be over-sized and installed to discharge to a nearby tank or drain. Minimizing pressure in the flush line will help optimize self-cleaning performance.

90 Series filters use 1-8 gallons, 180C Series filters use 4-16 gallons, 180 Series filters 15-110 gallons. Exact flush volumes will vary based on valve size, pressure, and filter geometry.

Flush Volumes by Filter Series

Yes, see the schematic below to review our dewatering system for backwash water recovery.

90 Series Dewatering System

2-30 seconds depending on the filter model and operating pressure.

TSS stands for Total Suspended Solids

What Are Total Suspended Solids


Screen sizes are available from 5 to 4,000 micron.

(Pictured below left to right): Perforated plate, wedge-wire slotted screen, multi-layered diffusion bonded wire mesh, and sintered mesh on perforated plate screens.

Industrial Water Filter Screen Types


Click on the chart below for preliminary recommendations by water source.  Water quality data including total suspended solids and/or particle distribution analysis provides the most precise method for screen selection.ApproximateMicronRangesForVariousFilterApplicationsbyWaterSource

Changing the screen on your Forsta Self-Cleaning Filter is quick, easy and requires no special tools. See below to watch the ~1 minute screen change on an ML3-90 series filter.


A particle size analysis (PSA) and total suspended solids (TSS) value (in ppm or mg/l) are required  to address this question. Particle size, concentration and total volume will dictate the solids reduction that can be achieved with any given screen size.  View the chart below to review a sample particle size analysis.

Sample Particle Distribution

Yes. The “filter cake effect” describes the fact that degree of filtration becomes finer as a screen accumulates dirt (differential pressure increases.)


In the case study shown below, data will demonstrate results of the filter cake effect in an industrial cooling tower system.


There is no minimum flow requirement for normal operation, but the minimum requirements for backwash are 40gpm.

Maximum flow rate depends on the degree of filtration and the amount of screen area. Max flow = recommended flow per sq. ft. x total screen area (When flow is not restricted by pipe size). Click on chart below for more information.

max recommended flow by micron

A minimum of 35 psi is required at the inlet of the filter during the backwash. Low Pressure Series self-cleaning filters require 15 psi at the inlet of the filter during the backwash.

Filters are sized for less than 1-2psi of pressure loss across a clean screen. See chart below for differential pressure by flow at various filtration grades.

DP v GPM Log

Backwash frequency will depend on the water quality and degree of filtration.

The filter can be inspected once every six months to a year.

Standard materials include epoxy-coated carbon steel and stainless steel 304L and 316L. High grade alloys including duplex, super duplex, and Titanium are available upon request. Fiberglass reinforced plastic is also used for high chloride environments such as seawater, produced water, and brine.

Yes. Forsta self-cleaning filters are customizable in material, orientation, flange spacing, screen type, motor, controller type and more. Advise Forsta engineers about the needs of your project and they will work with you to create a custom filtration solution.

Yes, Forsta has been approved as an equivalent for specifications naming a wide variety of vendors of automatic self-cleaning filters, automatic self-cleaning strainers, automatic brush filters, automatic suction scanners, auto backwashable filters, auto backwash strainers, etc.

Stock items may be assembled and shipped same day. Non-stock items usually ship in 4-6 wks.

Yes, contact Forsta Filters to find the installation nearest you.

Yes, small units may be piloted for a fraction of the cost of purchasing a large unit. Generally, some portion of the rental fee may be applied to the purchase of a larger unit.

Call us today at 310-837-7177 or fill out our contact form and we’ll be in touch with you right away to make sure your filtration needs are met!

Request a Quote