Racor housing puzzle

[Nick F]

I am relocating my Racor filters and took a closer look at how the housing works. (My filter units are model 900FG)

I was surprised to find that it appears that fluid could bypass the filter element by leaking past the threads of the "T-handle" clamping bolt which holds the lid down. I attach a diagram of the filter housing showing the leakage path. Please excuse the crudeness of the sketch!

Is anyone familiar with Racor housings? Can anyone tell me why I should not be concerned? Obviously I will be contacting Racor but I thought I would post here first.

 

[Jaep]

There is supposed to be an o ring on the t nut and a rubber gasket on the cover.

 

[Nick F]

There is supposed to be an o ring on the t nut and a rubber gasket on the cover.

There are - I show them in the sketch in red.

 

[luna]

You know I never thought about the run of the threads leak path despite multiple filter changes and a rebuild a number of years ago.

If you are moving yours they likely have the lids loose. Is the T handle threading into a blind hole?

 

[Iggy]

There are - I show them in the sketch in red.

Those two gaskets you should replaced at the same time as the filter.

 

[Nick F]

You know I never thought about the run of the threads leak path despite multiple filter changes and a rebuild a number of years ago.

If you are moving yours they likely have the lids loose. Is the T handle threading into a blind hole?

First off, thanks you Luna - finally someone is recognising what I am trying to explain!

The T-handle threads into the central hollow post. No, the hole is not blind - the bottom of the male threaded part of the handle is in contact with the outlet fluid.

When a vacuum gage is installed on the top of the housing the male threaded part of the T-handle is hollow to let the outlet fluid communicate with the gage. (Racor gage datasheet attached)

 

[TBill36]

What size particles do you think can leak past the threads when they are tight? Also, flow is going to follow the path of least resistance, and the filter elements are designed for least restriction. I'll agree there is a leak potential but wonder if in reality it matters.

 

[Iggy]

I was mistaken at what you were driving at. Short of replacing the assembly. What about tape or thread on the T handle. Of course, something not affected by the fuel.

 

[Gdavid]

I believe when you screw the lid down, the center of it should be tightly fitted on the tube, and while there is no gasket or o-ring there, it is assumed that it is sealed well enough. If your filter is relatively fresh, fuel flowing though it should be the path of least resistance rather than squeezing through that gap and chasing the between the main and female threads. Honestly I have never pondered this before

 

[Bmarler]

I’m sure that racor did testing when developing this housing. You would test the fluid coming out the exit for particle size.
Personally, I don’t believe that much, if anything will get by the threads when they’re properly set.
If anything did happen to get through, your secondary filter will catch it.

 

[Greg QS]

As per the spec sheet you provided from racor.
The threads in the area you specified are UNF threads.

UNF threads are also widely used in applications such as pressure vessels, pipe connections and hydraulic systems. These fields have strict requirements on connection reliability and sealing performance, and UNF thread can provide stable connection and good sealing effect.

It is a thread is considered self sealing. If it were not your vacuum gauge would never hold a vacuum.

 

[cafesport]

Greg nailed it. If you have ever wondered about the knock out hole on the top of the filter cartridge it’s a bypass hole because the housing wont flow fuel without a cartridge in place. Be extra careful not to cross thread the gauges or t handles when changing filters.

 

[BB-marine]

The threads are 9/16 18 UNF (fine thread). The complete housing is sealed. This means that everything inside the filter housing is in a vacuum. The path of least resistance comes into play. Is it easier for the fuel to pass through a filter element or a segment of fine threads? If it is easier for fuel to pass through the tee handle fine threads the filter would be plugged and the engine probably would not have enough fuel to operate.

This is a proven filter system I would not question its design.

Brian

 

[luna]

There are at least 3 Classes of threads within the UNF family.
Each class requires a higher degree of precision to ensure a tighter fit and as a result a higher strength.
All are parallel threads and none are an interference fit.
The threaded connection allows for reuse as if used correctly, no deformation occurs.
As a result, all will leak and all need a gasket or other method to seal the connection.

The only threaded connection that I know of that can seal without a sealant is the NPTF thread, that thread also has more than one thread Class. These threads reliably seal themselves completely by deformation, once.

I think the downside from the leak is quite low in this instance when you consider that the fuel level inside the filter housing is below the top of the tube, (the present 8' sea conditions are an unfortunate exception) the lid is likely quite tight and the vacuum is low.
That being said it is likely to leak.

This leak which occurs entirely within a sealed housing has no effect on the ability of the sealed housing to hold a vacuum. It is simply a path for (Edit, a very small amount of) the fuel to bypass the Racor filter and get to the secondary filter unfiltered.

Maybe, given all of the parameters this has just become the acceptable design solution.
When you consider that all of the spin on filters out there suffer from the same leak path except the start of their path is always flooded, the industry does not seem too concerned.

 

[Nick F]

. . . the level inside the filter housing is below the top of the tube, . . .

Thank you, Luna, for another well founded reply. I sounds like you too are a mechanical engineer!

However, I do not understand why you would say that there is air in the top of the housing. I always fill the housing right to the brim when changing cartridges. Would this be air that has found its way into the housing during operation and remains trapped there forever?

For info: I have sent a query to Racor. Let's see if I get a coherent reply.

 

[Nick F]

This is a proven filter system I would not question its design.

Brian

Thanks, Brian, but I learnt during my career as an engineer to question everything.

 

[luna]

Racor tells you to fill the housing to just above the top of the filter.
It carries on and says it's normal for the fuel level to drop during use.

See page 6 of this.

https://www.parker.com/content/dam/Parker-com/Literature/Racor/Tech_Install/19526_900MA-1000MA.pdf

I trust you will post Parker's reply, as I'm quite sure it will help all of us get a better understanding of what is going on here.

 

[Nick F]

I trust you will post Parker's reply, as I'm quite sure it will help all of us get a better understanding of what is going on here.

For sure - I like threads which have good close-outs.