Testing the Northern Tool Hydraulic Filter Head

[kd5byb]

Good afternoon all,

With all the discussions of the bypass valves in differing hydraulic filters being applied to transmission applications, I decided to do some testing on the Northern Tool hydraulic filter head I have.

I wanted to do two things - one, check the actual psi opening of the bypass. Two, assess how well the filter and bypass valve sealed.

To test the bypass, I needed to simulate a totally clogged filter. With the help of the hot-melt glue gun, I took the filter that came with it that I won't ever use and plugged up in the inlet holes on the top of the filter can:

Then I attached a 0 to 30 PSI pressure gauge to one of the gauge ports on the inlet side of the filter, and added a 3/4 to 1/4 NPT and a 1/4 NPT air hose fitting so I could apply air pressure:

Initially, I set the air pressure to zero. Then, I slowly increased pressure. As soon as the pressure gauge moved, I could detect air flowing out the exit port. As air pressure increased, the leakage increased.

I turned off the air and removed the filter, thinking what I had here was air leaking between the input and output sides at the filter thread. I added several turns of teflon thread tape to the filter thread, and reattached the filter.

Applied air, and the leakage continued. Again, I turned the air off and removed the filter, thinking that one of my glue holes was leaking. Inspected all of them and couldn't see an obvious hole that would account for the air.

So, my conclusion is that the bypass valve doesn't seal perfectly and will allow some oil to bypass the filter. I don't think anyone expected the bypass to seal perfectly, as its a piece of plastic pushing against a flat metal seat without any special surface preparation or sealing materials.

Next, I slowly increased air pressure upwards. As air pressure increased but stayed shy of the 15 psi mark, the flow was significant. While I was using air and cannot accurately guess the flow of a fluid, its definitely a significant amount.

At 15 psi, the amount of air exiting the output port increased markedly, indicating that the bypass valve had opened. We'd previously thought that the Northern Tool mounts were 15 psi bypass, and this confirms that.

My conclusions - there will be some oil leakage around the bypass valve. So even if the filter is totally full yet hasn't opened the bypass, you'll still get some flow but not a great amount.

thanks much,
ben

 

[Gary Allan]

Let's no see one swallow and call it summer. You've got some leakage in your bypass valve. That's about the limit of what you can determine with this mount. Run warm ATF through it and retest. You may find that it's not a leaker ..or you might. Right now it's a static "I did this ..and that occurred".

I'll add that it's good work for what it shows.

 

[dnewton3]

I'm not familar with this filter; does it function in the typical way that most do? In through the small holes, across the media, and out the large hole?

If you blind off the inlet holes, and everything is sealed correctly, you should get NO leakage because the air should be dead-headed against the glue plugs. You, in theory, would only be testing the seal of the large gasket, the teflon tape, and the hot glue on the holes.

I don't understand how you were trying to test the bypass valve? If you blind off inlet holes, then apply air to the inlet, how is it supposed to load the upstream side of the media?

Am I just not getting it? Isn't the bypass supposed to open only when the media is loaded? If so, how does blinding off the inlet holes, and then presurizing the inlet port of the filter mount test the bypass valve? You have put the "dam", as it were, in the wrong place.

I'm open to critisizm, but I don't think you're testing what you believe you are. The only way to see how well the bypass works is to non-destructively take a new filter apart (don't ask me how, I don't know), then hot glue the entire filter surface, then put it back together (again, don't ask - I don't know). Then pressurize the inlet, and force the air across the bypass because the media would hopefully not pass the air.

BTW - I worked for 16 years at Ford's powersteering plant. Testing with air and oil are NOT the same thing. Air molecules are much smaller than oil molecules, so you can't presume that an air leak would show up as an oil leak. I understand that you're just using air as a pressure medium because it's clean and readily available. But, air will get past places that oil won't. In fact, did you think to lightly oil the entire gasket seal before you ran the filter up to the mount? It looked dry in the photo. And you have to oil boths sides of the gasket; in other words, take the gasket off the base, oil the side that faces that base and the side that faces the mount. Air will escape places that oil can't even begin to imagine. We used to pressure test our steering units to 90 psi and find seal leaks that won't show up with oil. In fact, we could detect air leaks due to housing porosity, that oil wouldn't flow through.

I believe the air you're sensing is not at all going past the bypass; it's likely escaping past the teflon tape seal and/or the glued inlet holes. It's possible, but not likely due to the volume of flow you're describing, that the mount may have porosity too.

I think you need to go back to the drawing board.

 

[dnewton3]

Ok - did I just get blazed? Was this a joke?

I just looked up the Wix x-ref (51551). THERE IS NO BYPASS VALVE ON THIS FILTER. Makes sense actually, becuase lot's of hydraulic filters don't have a bypass.

Makes my previous points even more valid; you're leaking across the teflon tape or the glued holes!

 

[deeter16317]

I was going to ask why you used a filterhead with a bypass valve, when they sell them without the bypass valve??

Most hydraulic filters have no internal bypass valves (unlike a car's oil filter)...

Something else to keep in mind is that you could change the breaking pressure of the valve??

 

[dnewton3]

I think I understand now, what he was trying to test. I figured it out after I read a post in the ATF forum section regarding this same topic.

When I first read the OP, I took his statements to mean that he was checking for bypass valve function in the filter, when I believe he's actually got a filter mount that has an integral bypass in it. Makes a lot more sense re-reading it now. Clearly my mistake in reading the OP too fast.

I don't really understand the benefit to having a mount with a bypass in it. I would prefer a bypass valve in the filter itself. If the bypass valve works (in filter or mount) there shouldn't be any issues. But think of the reverse; what if the valve were to fail. There are two ways for a valve to fail: not open when it should, or open when it shouldn't. Either way, if the valve is in your filter mount, you have more work, money and time in fixing it than if the valve is in your filter, which is a quick, inexpensive swap. Neither condition is favorable, but one is just cheaper and easier to fix.

 

[Gary Allan]

There are 1-12 thread automotive filters that have internal bypass valves. They fit Jags and like engined Lincolns. They aren't as fine as hydraulic filters.

..but the mounts are very cheap and can compete with the costs of the filter depending on distribution. You're talking $20 delivered for a filter/mount combo. The mount alone is $7.99+ some minimum S&H ..so essentially you're getting the filter for $6

I would like to see him place the filter in boiling water (mount and all) and retest. He may find that the bypass valve seal is more sealing when at temp.

OTOH, he may just have a defective seal.

 

[dnewton3]

Now that I've removed my head from my posterior, and understand this is a bypass in the mount, I'd agree.

My point of air vs. oil for the test is still a significant suggestion. Air and oil just behave so differently when under pressue. Pressure is always all equalizing, but it's the way they react to pressure that seems odd at times.

I would presume the bypass valve is just a simple spring loaded plunger pushing the seal against the seat. With that in mind, I would think the seal material and it's subsequent reaction to temperature would be the greatest controlling item in his test. Air would likely seep around the seal where oil would probably not, until the spring pressure was overcome.

ON a side note; is the reason for the bypass valve in the mount to relieve cost from the subsequent filter purchases? I can't imagine any other reason than that of cost. But it places the burden of bypass to the mount. As I stated, I'd rather have a bypass in the filter in case it goes bad, it's easier to replace.

 

[Gary Allan]

In my playing around in this realm, I've found that there are two basic variables in hydraulic filtration...micron level and bypass threshold. It must make sense to the powers that be to make several mounts for each thread with various bypass levels than it would be to make a dozen filters with various bypass valve settings that were otherwise identical.

Hydraulic filtration appears to be (mostly) divided by pressure class. As you graduate to higher pressure, the threads change a bit ..but the constants are the bypass thresholds. This, again, makes sense from and economic basis. Buy the mount for the intended application ..sell universally applicable filters.

Some applications have no bypass provision in the mount. That is, some may desire no bypass valve.

 

[kd5byb]

Hello all!

Some comments on the past few threads. I'd reply individually, but that would be a pain.

The main goal of my test was to see what delta PSI would be required for the bypass valve on the Northern Tool head to open. It had been postulated to be 15 PSI and the test showed that my unit is very close to 15 PSI, if not dead on. For this test, it shouldn't matter much what test medium I use - pressure is pressure.

Now, I totally agree that *amount* of leakage around the bypass valve will depend on the fluid used. Air was used for the test because it's easy. ATF, especially warm ATF, will leak at lot less, and may even not leak at all.

I bet that it still will leak - the key is how the bypass valve is made - it's a plastic disc held against a die-cast opening inside the head by a spring. There is no machining of the area where the bypass valve affects a seal, so some leakage is to be expected as it isn't really made to make a perfect seal.

Certainly, it will leak a lot less warm ATF than air!

Yet, the seal doesn't need to be perfect - some leakage of a small percentage of the fluid past the filter doesn't hurt filtering efficiency much when we look at this filtering system being multiple pass with a small sump and low rates of debris generation. I may miss 1% of dirty fluid on the first pass, but on the second pass, only 1% of 1% makes it through, and so on. Of course, this neglects dirt production in the transmission, as I assume that its negligible in the short term. I think the thing to remember is that regardless, we're filtering the fluid to a much finer level than the in-transmission filter and that's goodness.

It's still goodness even if I filter only 50% of the fluid per pass.

(Side note - I have some heads that have NO bypass valve. I've thought about drilling a hole, perhaps 1/4" hole between the input and output sides. The majority of the flow is undisturbed, while some amount is diverted through the filter. Even if I only filter 10% of the fluid each pass, my fluid will still be far cleaner than if I had no external filter. I'm seriously considering this idea - no bypass to fail, no real pressure rise, etc...)

I found the leaky seal to be an interesting revelation, as people had been talking about these $15 or less filter heads as having perfect seals, which they do not! Not only does the bypass valve leak a little, but there will be some terribly minor leakage around the filter's thread. It's not a perfect seal.

As to the bypass in the head versus the bypass in the filter - this may be a Ford/Chevy kind of debate.

Most of the fine (beta 2/20 = 5/12 or better) filters I've seen are hydraulic filters that don't come with internal bypass valves. I can't say why they chose to put the bypass in the head. I can't say why most auto filters do the reverse! I will note that with the recent trend back to cartridge filters like in my Tundra, it seems that the bypass valves are leaving the filters and going back into the non-disposable part of the oil filtering system.

The bypass valve in the filter head is a simple spring/plunger system that is pretty bulletproof. I can say the same thing for the bypass valve inside a filter too. How many millions of cars today depend on the in-filter design?

I don't see an in-head bypass valve failing any more than a valve inside a filter. For an in-head bypass, you're betting against a long-term failure mode - breakdown of the material used, failure of the seal, etc... For an in-filter bypass, you're better against an infancy failure mode in a bum filter made on a Friday before a three-day weekend. Or, on a Monday morning after a three-day weekend.

The only advantage I see is that I can easily visually inspect the bypass in my filter head when I change filters. I can't inspect the bypass in an internally-bypassed filter at any point without the destruction of the filter. We can debate how effective a visual inspection is, but that's way in the weeds, even further in the weeds than I already am!

Another advantage to having the bypass in the head is that I can separate the bypass from the filter. IE: I can have a 3 psi, a 5 psi, and a 15 psi head that all can use the same 10 micron hyd filter. For an internally-bypassed filter, I need three different filters to do this.

You can turn that right around too - the filter guy will say that I now have to have three different filter heads for the same filter to get the three bypass ratings above!

All I can say is that you've read this far, my hat's off to you! I'm extremely verbose this evening.

thanks much,
ben

 

[XS650]

Quote:
Most of the fine (beta 2/20 = 5/12 or better) filters I've seen are hydraulic filters that don't come with internal bypass valves. I can't say why they chose to put the bypass in the head.


It's a simple reason. Hydraulic oil filter installations are much more custom installations than automotive oil filters. The hydraulic installation designer will select the bypass pressure based on his system requirements. It makes more sense to manufacture a head that can be set for different pressures by changing a spring than it does to manufacture umpteen different version of ewach filter to supply different bypass pressures.

 

[Shaman]

XS650, are those springs readily available if someone wants to change them?

 

[kd5byb]

Originally Posted By: Shaman
XS650, are those springs readily available if someone wants to change them?


I've been meaning to write PTI and some of the other manufacturers (perhaps PFC) asking the same question. Not sure if they will or not. Seems like they'd say to just buy another head with the right spring, which isn't an option when you're buying surplus off of eBay or new at Northern Tool to keep things inexpensive.

BUT, I may have lucked into something neat! The other day, I was in a Northern Tools store buying my two year old son a Radio Flyer Wagon for XMAS.

I wandered into the hyd filter aisle and ended up bringing home one of the larger size hyd filter assemblies (item 4022, shown with filter removed):

Mostly, I did this on a lark! I was pretty convinced that the smaller NT filter head was ideal for transmission applications. But, for $25 and no shipping (I was at one of the stores) I figured what the heck.

It has an unusual bypass valve - it has a threaded screw and a nylock nut. By adjusting the nylock nut, it appears that you can vary the bypass valve spring preload pressure! Hhhhhmmn!

Nut and spring on output side of the filter: (photo brightness turned up to show spring coils better - the whole spring is tapered like a Christmas tree - wide base, small top!)

Valve viewed from the inlet side of the filter:

I'm going to fool with it and see if I can adjust it down from the stock 15 psi to more like 5 psi. If so, this seems like it might be the perfect mount. Don't like the stock pressure? Adjust it to what you want! As Jack from Jack's Big Music Show says, "Dance how you like!" (When you've got a two year old, you watch all the kiddy shows.)

It looks like it can mount some really wicked fine filters, such as the Wix 51746:

Part Number: 51746
Principal Application: Cat, Ford/New Holland Equipment (5 Micron)
Style: Spin-On Hydraulic Filter
Service: Hydraulic
Type: Full Flow
Media: Paper
Height: 6.872
Outer Diameter Top: 5.007
Outer Diameter Bottom: Closed
Thread Size: 1 1/2-16
By-Pass Valve Setting-PSI: None
Beta Ratio: 2/20=2/7

Burst Pressure-PSI: 335
Max Flow Rate: 28-30 GPM
Nominal Micron Rating: 5

NOTE: I haven't tried this filter on this head, yet. However, I have a PTI filter head that takes the 51746, and the stock NT filter fits well on this PTI head. So, I assume that the reverse will be true and filters like the 51746 that fit the PTI head will fit the NT head.

Only problem may be the diameter of the gasket furnished with the 51746. Might take a 15661 gasket instead of the 15386 gasket that comes on the filter...

later,
b

 

[XS650]

Originally Posted By: Shaman
XS650, are those springs readily available if someone wants to change them?


I doubt that they are readily available to John Q Public.

 

[Gary Allan]

Quote:
Only problem may be the diameter of the gasket furnished with the 51746. Might take a 15661 gasket instead of the 15386 gasket that comes on the filter...


Filters of this size class appear to come with a number of gasket options. I assume that's so that it can fit a few different mounts within reason.

Part Number: 51759
UPC Number: 765809517592
Principal Application: Various Hydraulic Applications (Hydraulic Version of 51758) (10 Micron)
All Applications
Style: Spin-On Hydraulic Filter
Service: Hydraulic
Type: Full Flow
Media: Paper
Height: 6.872
Outer Diameter Top: 5.007
Outer Diameter Bottom: Closed
Thread Size: 1 1/2-16
By-Pass Valve Setting-PSI: None
Beta Ratio: 2/20=18/38
Burst Pressure-PSI: 360
Max Flow Rate: 28-30 GPM
Nominal Micron Rating: 10

Gasket Diameters
Number O.D. I.D. Thk.
15415 5.140 4.750 0.195
15658 8 5.055 4.480 0.359
15661 8 5.030 4.440 0.190

I have 3 of this size filter. Naturally I'm having fun finding a place to use them ..but it's very hard for me to pass up salvage prices for high quality industrial grade stuff when I can buy it for less than a dime on a dollar

Edit: The mount(s) pictured have the same nut to adjust the spring tension ..or so it appears. My spring is not tapered, however. I'm not sure, but the nut may be a nylock type.

 

[kd5byb]

Agreed - seems that many different gaskets allow the fitting of a wide range of filters.

In fact, Wix specs the 51759 as being a replacement for the Buyers filter that comes on the large (item 4022) NT filter head. BUT, it seems that per my measurements, the o-ring that comes with the 51759 (p/n 15415) is not the right size for the large NT head.

Looks like Wix 15661 is the right size. But, I'm having a heck of a time finding anyone who sells the 15661 gasket, ugh!

BTW, those Norman filters seem to be NICE!

later,
b

 

[Gary Allan]

I couldn't resist them for $20 ($40 for two delivered).

Gauges and all. They're HUGE. Oddly, the cans themselves are quite light compared to another (shorter) filter I picked up in the same thread/head size.

 

[kd5byb]

Nice price! I would have had a hard time passing them up for $20 each as well. Any idea what their original application was?

Interesting...

later,
b

 

[Gary Allan]

I have no idea what they were intended for. They're from a liquidator. Norman Filter is the company ..and they sell the entire filter http://www.normanfilters.com/page9.html

 

[Tempest]

The Northern unit that I am running gets hot quick, so there seems to be little if any bypass problems.