The 550 used three styles of fuel valve/filter combo.
The first in 1974 was just like the Cb500 valve/filter. It had/has a sediment bowl and a screen to stop particles of certain size and larger from entering the fuel stream to the carbs. Any filter will have a particle size rating. And, the stock screen traps anything that won't fit through any metering orifice in the carbs. I maintain that if the particles can flow all the way through the engine it really isn't much concern.
In 1975 the fuel valve changed and there was a "sock type" filter and stand pipe combo made of nylon (I think), which fit into the tank bung. The bung was about 3/4 inch diameter.
This type avoided regular servicing intervals, and it still blocked particles finer than would fit through the carbs. Further, the fuel sloshing washes the sock membrane to keep it flowing. Sediment CAN still build up in the tank. And if varnish builds up on the sock, from long periods of stale, rotten, fuel sitting in the tank, the tiny pores can be blocked. Any machine can be destroyed by man.
In 1977, yet another fuel valve design was introduced. The tank bung size was reduced to about 5/8 diameter, and a more rigid and robust nylon based filter tube was placed in the tank, surrounding the metal stand pipe tube that protrudes from the fuel valve.
As before, the filter is self washing to maintain flow. It still can fall victim to varnish and neglect.
I have examples of all these filter types, and they still work as new after 30-ish years. But, they also had periodic fuel replacement, to keep varnish from occurring.
The varnish makes the sock brittle so it cracks or tears upon removal. It probably can be saved if soaked in carb cleaner before extraction is attempted.
If the tank is rusty, jagged bits can also damage the filter sock.
The nylon tube type can be very difficult to extract from a rusty and or varnished tank bung. It takes patience and the appropriate chemicals to either remove the rust first, or dissolve the varnish before extraction is attempted.
It seems few have this sort of patience. And, I am guilty of destroying a couple before I learned what the issue really is with aged, neglected components needing restoration.
How many people would think of soaking the in-tank filter in carb cleaner for a day, and then some metal prep to convert rust, BEFORE removing the fuel valve and filter?
When in a hurry, damage often happens.
Hope this helps,
