There are basically three fuel filters (four if you count both tanks and six if you have a model with two screens in each tank.) in the standard 210 fuel system. Each fuel tank has one or two fuel ports, depending on the model, each having a very coarse screen called a finger screen. This screen is coarse enough to allow something the size of a “BB” or flakes of old tank sealant to pass. The finger screens are buried in the bottom inboard of the tanks and not accessible during routine inspections.
The next filter is in the gascolator, which is mounted forward of the firewall. Most gascolators are mounted on the left side wall in the nose wheel well. The later N models and R models mount the gascolator on the left lower firewall. These are all easily accessible and almost always removed for inspection at annual time. It’s very common to find the gascolator bowls corroded due to lack of being drained during every preflight to remove the up to three ounces of water that can accumulate there.
The filter that too frequently gets ignored during annual inspection is the fuel servo inlet screen. This is the last chance filter to protect the fuel controller, engine driven fuel pump, flow divider and the fuel injector nozzles.
The servo screen is a cylindrical shaped metal filter buried at the back of the engine mounted in the fuel control assembly on the Continental sandcast engines (IO520 and TSIO520 series). Access to the filter requires the mechanic to navigate past the ship’s battery on the left firewall and around the rear alternator. Pressurized aircraft add plumbing from the induction venturi to the cabin heat exchanger just to add a little more challenge. For those still using pneumatic instrumentation and/or pneumatic de-ice boots, the fuel controller is just below the pneumatic pump(s) and all their plumbing.
The space available often only allows working with one hand and possibly without being able to see the filter at the same time one is installing it. The filter is safetied in place which adds to the skill level and tenacity required to remove and reinstall. Of course, it also must be tightened with a torque wrench prior to installing the safety wire which is difficult to achieve in the tight quarters.
Inspecting all filters should be a standard part of every annual inspection. It is not uncommon for us to find the engine manufacturer’s, or engine overhauler’s, original safety wire still installed on these screens several years and hundreds of hours of flight after the engine was installed. We can’t be sure why this screen is so often ignored during annual inspections. It could be ignorance of the filter’s existence, unwillingness to make the effort to access it, or disbelief in the importance of inspecting it. Regardless, as the aircraft operator, you want to ensure this filter is inspected and cleaned at every annual or 100-hour inspection. Asking for a photo of the filter prior to its being cleaned not only gives confidence that it has been inspected but also lets you monitor any trends in the debris amounts found.
Copyright © Paul New 2021. All rights reserved.
Hi Paul! Great article! One thing I’ve had difficulty finding is the part number for the crush washer that seals that screen to the assembly. Have your guys had success in obtaining a good replacement?
Thank you! There are different size washers. The Continental Engine Illustrated parts catalogue for your particular engine will have the part number for the crush washer.
With the overhead induction system on the Summit Aviation IO550 conversion for the Cessna 210, where would the fuel servo screen filter be located.
That engine does not have a fuel screen on the engine fuel controller. The last filter in the system will be the gascolator.