Vacuum gauge downstream of OEM filter?

[Jim Cobler]

I have been doing some research on putting a vacuum gage between the OEM filter and the engine. The regular vacuum guage companies that I have contacted have said that most regular automotive vacuum guages are in inches of mercury. These will not work. They have suggested that I contact a company that sells industrial guages that are measured in inches of water.

If I have understood what has been said here, the guage would have to measure from 0 to about 15 inches of water. Is this correct? Any ideas on who might sell these?

Thanks,

[pinehill]

No, you want a guage which will measure vacuum in the range of 0 to about 10 inches of MERCURY (Hg).

[BigLakeDMAX]

Jim,

I concur with Pinehill that we want inHg as the scale. inH20 is also a scale used for measuring vacuum, but my research has indicated that inHg is the more applicable scale. The two measures are convertible, as 1 inHg = 14 in H20 (actually, 13.5951 inches with a water temperature of 39.2 degrees F).

I'm working on this same project - email me if you want to discuss the particulars - I'm saving most of the details until I know more if my idea will work.

dabbott@sherbtel.net

Take Care,

Don

[mdrag]

The borrowed J44638 fuel restiction gauge that I've been using is a combination gauge with the following range:

0-10 psi
0-30" Hg

The restriction measurements that I obtained so far:

Normal/Fast idle speeds
OEM Racor w/1.6K 3.0/3.5
New OEM 2.5/2.75
New OEM/Baldwin Mega secondary 3.5/3.75

IIRC, a recommendation was made to change the filter when there was an increase of 7-8" Hg. The psi side of the gauge could be used to pump up the system (using the primer) to see how fast the system drops pressure.

In my limited experience, I was able to pump up to 10 psi using the primer, and the pressure held for 1-2 minutes, and then slowly decreased to 0. I plan to explore this in closer detail.

If anyone finds a source for a gauge with this range or close to it, I'd like to get one.

[Lone Eagle]

You really need to know if the pump manufacture rated his pump in HG or WC. If all you want is to compare before and after reading I would us a water colum gauge. It will be highter up on the scale where it is easier to read. Later! Lone Eagle

[mdrag]

Lone Eagle,

Just to clarify, the J44638 fuel restiction gauge has a dial indicator, approx 4" in diameter. Zero is located at 1 o'clock. The needle moves clockwise to max 10 psi at the 5 o'clock position; counter clockwise to 30" Hg at the 6 o'clock position.

For reliable accuracy, you should use a gauge with the proper range so the readings are not obtained at the extremes.

[ 03-19-2003: Message edited by: mdrag ]</p>

[a bear]

mdrag,
20%-80% of the gauge range is considered the accepted industry standard for measurment. By the way my pressure also fell after a couple minutes. Not sure if this is normal or not. It appears to be going back into the system. (no leaks detected) :eek:

[TraceF]

Someone please tell me what IIRC means.

Signed, Dummy

[Flyboy]

TraceF IIRC = If I Remember Correctly.

[Lone Eagle]

[ 03-19-2003: Message edited by: Lone Eagle ]</p>

[Lone Eagle]

mdrag, I understand what you have. I have used and installed quite a few compound gauges. Did you mean .7 to .8 increase across the filter? Later! Lone Eagle ;)

[Lone Eagle]

a bear, I would think the pressure drop would be normal. It is almost impossible to trap hydraulic pressure. It probably went right through the pump. Later! Lone Eagle

[mdrag]

a bear,

I believe we will see that this is normal. It appears that we are seeing similar results.


Lone Eagle,

That would be 7.0" - 8.0" Hg increase.

From a recent post by Kennedy:

http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic&f=3&t=005344&p=1


FWIW, even that "monster" of a filter that I use will add a MEASURED 1" hg. (approx) of restriction to the 2"hg already existing in the system with a NEW OE filter.

When I hit 10k OR 5-7"hg on my filters (both installed about 4k ago) I will change the OE unit first and check the drop in restriction. If it normalizes, I will continue use of the same element on the Mega kit and push on. If it still shows significant restriction, I will change the element. I am hoping we can go 15-20k on the Mega element..


mdrag

[pinehill]

mdrag,

I had interpreted JK's 5-7" statement as a TOTAL limit, i.e., not as an addition to the 3.5" or so of a fresh installation. :confused:

[ 03-19-2003: Message edited by: pinehill ]</p>

[Lone Eagle]

mdrag, I read John's post. He said when he reads 5 to 7 Hg he will change a filter. I sure would like to know what is the max suction head before cavitation. Later!

[BigLakeDMAX]

mdrag and a bear:

The Helms manual indicates that you should use the primer pump to achieve 8 psi and it should not drop below 2 psi in less than two minutes. If I'm reading it correctly...

Sounds like your results are fine. Couldn't find anything about a maximum recommended vacuum, though.

[Kennedy]

I've seen the rate of drop vary. Mine was much quicker than Coldfront's 2003, but since dropping is normal, and I could find no leaks, it must be fine. My truck has almost 35k on it and his had just over 1k.

The 5-7"hg figure was based on what I have seen an OE filter restrict to at 15k. I figure this is a significant increase in restriction, and that if I replace the OE filter and see a large drop, I know that my secondary is good to go some more...

[mdrag]

I spoke with Kennedy about the filter restiction readings to clarify statements above. Kennedy told me that he obtained a reading of 7" Hg on on OEM Racor with about 10K miles on it.

The plan - for now - is to change the OEM Racor when the restiction hits 7" - 8" Hg reading.

So, as an example, with a new OEM and new Baldwin Mega secondary, I obtained 3.5"/3.75" Hg reading at factory idle/fast idle - and will change the OEM Racor when these figures approximately double to the 7" - 8" Hg range.

Please understand that these values MAY change as more experience is gained and better information becomes available.