The Home Machinist!

Wow. They don't make 'em like they used to, sad to say. The new one is ugly too, but OK though, if it doesn't leak I suppose. Doesn't look like Donaldson stuff used to, that's for sure.
It appears the new & old are from two different manufacturers, as there are obvious differences in the castings.

The 'check valve', is the 25 psi element bypass valve. It prevents the element from collapsing internally when it becomes plugged up. That's why a gauge is a good idea. Larger Donaldson filter heads have optional indicators, rather than requiring a gauge, which serves the same purpose.
Looks like the plastic cage broke, or the spring partially fell off the cage.

Glad you got that solved!

Other Bill

Pardon my french ..but what a crappy looking sealing surface

Here's a pic of a Donaldson HMK05. Note the seal land is shiny. I've used 3 or 4 kazillion of these, and HMK25's, which are a double filter.
That's how seal lands are supposed to look, but too many people are making things on the cheap these days.....sad to say Donaldson is included.
Other Bill

A big difference. I'd be tempted to chuck up that replacement and machine the face flat.

Greg_Lewis wrote: ↑Thu Jan 06, 2022 7:41 pm A big difference. I'd be tempted to chuck up that replacement and machine the face flat.

That’s what I’d do, not to mention what I have done or had done in similar circumstances.

Prescribed finish for any o-ring sealing surface is 32 RMS. That includes surfaces for square cut o-rings. They missed that day in class. Those filter heads look to be more like 300-400. Ugly.

Other Bill

Hi, if this base leaks, how would one go about milling the surface?

Geochurchi wrote: ↑Fri Jan 07, 2022 11:15 am Hi, if this base leaks, how would one go about milling the surface?

Chuck it in a 4-jaw chuck on a lathe, centering it on the diameter of the alleged o-ring surface.

That’s above our pay grade, first I have to see if this new base leaks , won’t be around for a week or more, if I wanted to check the pressure on this system I assume I could use one of the ports on this base, HP side.
Geo

It could be done with a mill too, if you have one.

Both gauge ports are in the inlet side on that filter head, so pick the one that' suits you best.

Download this: https://www.donaldson.com/content/dam/d ... -Guide.pdf
Pages 16-19 for your filter assy. Everything you want to know, whether you were afraid to ask or not!

If the new one is also NPT porting, be sure you use pipe dope on the adapters. The teflon type works best for hydraulics.

Other Bill

Update, after replacing the filter base and new matching filer the leak has finally been resolved.
Thanks for all the input, I am sure I will be back with other issues.

Good news! Thanks for letting us know!

Not only was the filter leaking, upon further inspection after we raised the locomotive up there was a couple of loose fittings on the pump.