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Information you need to know before selecting a filter assembly

Information you need to know before selecting a filter assembly

There are seven basic questions that need to be understood and answered before sizing and ultimately selecting the proper filter.

  1. What are you filtering?
  2. What is the flow rate (eg 30 GPM)?
  3. What are the pipe sizes (inlet/outlet)?
  4. What is the operating pressure?
  5. What is the operating temperature?
  6. What is the micron rating?
  7. What are the space limitations?

The above seven questions not in any order of importance, if understood and answered correctly, will greatly decrease the filter options available to you and will therefore reduce your work time significantly.

1.    What are you filtering?

With the fluids and additives available in today’s market, chemical compatibility plays a significant role in filter selecting. The fluid in your system may require a very cost efficient paper element in carbon steel or aluminum housing but with a corrosive fluid the use of a completely stainless steel element and housing may be required. The later will be a very costly option and should be chosen only when the fluid compatibility restricts you to do so.

The viscosity of the fluid in question will affect the size of the filter. Viscous fluids require filters to be sized larger in order to maintain an acceptable (minimal) pressure drop.

2.    What is the flow rate?

Most often the flow rate (Q) of a system will be either provided in gallons per minute (GPM) or liters per minute (LPM). The flow rate of a system will be an effective means of determining the size of filter to be used. There are a few other factors (micron rating, space limitations and viscosity) that will influence the size of the filter but will be discussed separately.

The equipment manufacturer or pump manufacturer will have specifications for the fluid system, the flow rate being one such specification. Build in a safety factor by always sizing the filter liberally or size to the maximum flow that will be seen in the system. This will take into consideration normal operating conditions as well as flow surges or spikes in flow. Trying to save money by sizing to normal operating conditions may result in flow restrictions and eventually component failure, associated component replacement costs as well as cost of non-productive equipment down time.

3.    What are the pipe sizes?

The port size of the filter that may be in consideration for the application you require may not be ported in a manner that is suitable for such application. In other words the piping already in place may be 1 ½”.  With all other factors being taken into consideration to maintain a flow of 30gpm do not choose a filter with a ¾” inlet/outlet as this will bottleneck the flow. Try to maintain a constant pipe to port dimension.

4.    What is the Operating pressure?

Similarly with flow rate, the normal operating pressure of the system either in pounds per square inch (psi) or bar (14.5psi) will be an effective means of limiting the filter options available to you. If system pressure can be as much as 3000psi a filter in the pressure loop with a burst pressure and/or a working pressure below this level cannot be used. Once again it is important to build in a safety factor to prevent catastrophic equipment or system failure. System pressure is not only a consideration for the pressure side. For example, an undersized filter on the suction side may result in costly pump cavitation.

5.    What is the operating temperature?

The operating temperature of the fluid in the system being filtered is an important consideration similarly with fluid compatibility. The three main seal types for element and filter housing are Buna (-40°F to +225°F), Viton (-20°F to +300°F) and EPE (Ethylene Propylene -55°F to + 300°F). Because of pricing considerations but limited by fluid compatibility and temperature ranges Buna is the standard seal type.

6.    What is the micron rating?

The micron rating or particulate removal efficiency that will be required should be specified by the equipment manufacturer but also take into consideration the customer’s recommendations as they may have a target fluid cleanliness that exceeds the manufacturer’s recommendations. The micron rating of the element may not appear to be an important consideration in regards to filter sizing but a further examination will prove otherwise.

The more efficient an element the more restricted the flow will be to achieve this greater efficiency. In order to achieve high efficiency and maintain proper flow the filter will need to be sized accordingly. The filter assembly will have to be larger for a 3µm element to flow the same as a 25µm element, all other factors being equal. The flow characteristics at an available micron rating should be available from the manufacturer.

7.    What are the space limitations?

For some applications the “sky is the limit” with respect to space limitations. This is the exception, not the rule. As “space savings” becomes a factor, pipe work becomes more intricate and available space for filter installations suffers. Maximum flow must be maintained but efficiency cannot be allowed to suffer in most circumstances.
Bear in mind that after the filter is installed at some point in the future the element will need to be replaced therefore requiring the filter assembly to be located in the most user friendly location as possible.

By understanding the above questions you will be better suited to supply your customer the appropriate filter assembly or at least be better suited to inform your supplier to provide you with the appropriate filter assembly.