#21  
Old 03-23-2023, 07:57 AM
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I personally would believe Doug Roe's book "Rochester Carburetors" and the info in it over any published comments / videos from secondchancegarage.

Doug Roe and Mike Urich understood how carburetors and fuel systems actually worked.

Tom V.

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  #22  
Old 03-23-2023, 08:26 AM
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Atmospheric pressure is a motive force that acts on fluids. But it takes a differential to cause movement. Whether it's the piston moving down the bore (creating a pressure less than atmospheric in the bore) or the diaphragm being pulled down by the pump lever (creating a pressure less than atmospheric in the pump chamber). It was stated by self-proclaimed engineers/experts that "There is NO suction going on in a mech fuel pump.". This is just NOT true. There may be a very slight measurable pressure less than atmospheric. That's because of very little restriction to flow by design. But it IS producing suction/vacuum. Pressure or vacuum is a measure of resistance to flow. The Doug Roe excerpts back up my claims. They don't contradict them. Read it again slowly.

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Old 03-23-2023, 09:12 AM
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Read your own post: "There is NO suction going on in a mech fuel pump."
Read your words here:

"There may be a very slight measurable pressure less than atmospheric."

You just contradicted yourself in the same post.

"NO" vs "may be"

But I am not going to discuss basic engineering principals with a guy who "Double Speaks"out of both sides of his mouth.

Tom V.

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Old 03-23-2023, 09:40 AM
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"There is NO suction going on in a mech fuel pump."

This is in quotations. It is me quoting Kenth. You back it up with "TRUTH". You seem to have lost control of your faculties sir. You're incapable of reading comprehension. No point in debating with you. Good luck to you.

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Old 03-23-2023, 09:51 AM
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JSchmitz,

Thank you, I'm well aligned with your description and appreciate another perspective.

We all understand it's differential pressure that moves fluid.

The differential in my car's fuel system is created by the pump diaphragm. The atmospheric pressure acting on the fluid in the tank does not change. It is static and therefore not the source of the differential.

The pressure inside the pump has to be lower than atmospheric pressure in the tank or the the fluid would not move from tank to pump. I call this suction. Others may not.

And I understand your comment about "a slight measurable pressure less than atmospheric". The differential is small because there is little resistance to flow. The gas flows quickly to eliminate the pressure differential created by the moving diaphragm... so fast I'm not really sure it could be measured, at least not with a mechanical vacuum gauge.

The only other way to create differential pressure between tank and pump is to pressurize the tank. This is not happening with a mechanical pump and a vented tank.

This is not worth a water fight post squabble in any way and I appreciate everyone's contributions to "how to prime a mechanical pump". I personally got the answers I needed and regret asking about suction.

My pump is primed and I'm happy about it.

Mike

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Old 03-23-2023, 10:24 AM
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Quote:
Originally Posted by Shiny View Post
JSchmitz,

Thank you, I'm well aligned with your description and appreciate another perspective.

We all understand it's differential pressure that moves fluid.

The differential in my car's fuel system is created by the pump diaphragm. The atmospheric pressure acting on the fluid in the tank does not change. It is static and therefore not the source of the differential.

The pressure inside the pump has to be lower than atmospheric pressure in the tank or the the fluid would not move from tank to pump. I call this suction. Others may not.

And I understand your comment about "a slight measurable pressure less than atmospheric". The differential is small because there is little resistance to flow. The gas flows quickly to eliminate the pressure differential created by the moving diaphragm... so fast I'm not really sure it could be measured, at least not with a mechanical vacuum gauge.

The only other way to create differential pressure between tank and pump is to pressurize the tank. This is not happening with a mechanical pump and a vented tank.

This is not worth a water fight post squabble in any way and I appreciate everyone's contributions to "how to prime a mechanical pump". I personally got the answers I needed and regret asking about suction.

My pump is primed and I'm happy about it.

Mike
Very well stated. I hope that I helped in some way. Good luck with your car!


Last edited by JSchmitz; 03-23-2023 at 10:24 AM. Reason: typo
  #27  
Old 03-23-2023, 02:51 PM
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Quote:
Originally Posted by Shiny View Post
We all understand it's differential pressure that moves fluid.

The only other way to create differential pressure between tank and pump is to pressurize the tank.
Hmm, seems that you, and JSchmitz, are missing that the tank IS pressurized by the atmospheric pressure, AND less than atmospheris pressure (a void where the fuel is pushed to by the 14,7 psi atmospheric pressure) is created by the fill side of the fuel pump when the membran moves down?
Everything on Earth is pressurized by the atmospheric pressure, so to move fuel from a tank to a carb you need to create a vacuum (void) for the fuel to enter in the fuel pump. On the other side of the fuel pump membran fuel is positively pushed to the carb.
Think again, it ís simpler to understand and explain the priciples of the combustion engine using the correct terms.

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Old 03-23-2023, 04:43 PM
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What kind of drugs do you folks take? Seems you all like to argue about making a distinction without a difference. Just to be "right" or not recognize when you posted something ignorant.


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Old 03-23-2023, 06:06 PM
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Shaking my head and backing away slowly...

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Old 03-23-2023, 10:06 PM
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3 tests for engine-driven fuel pumps, generally performed when the engine is turning via the cranking motor:
1. Output pressure
2. Output volume
3. Vacuum/reduced pressure created on the inlet side. (And the ability to HOLD that vacuum for a reasonable amount of time.)

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Old 03-24-2023, 05:55 AM
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Quote:
Originally Posted by Schurkey View Post
3 tests for engine-driven fuel pumps, generally performed when the engine is turning via the cranking motor:
1. Output pressure
2. Output volume
3. Vacuum/reduced pressure created on the inlet side. (And the ability to HOLD that vacuum for a reasonable amount of time.)
Question: Is #3 to test and see if it's holding atmospheric pressure? LOL!

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Old 03-24-2023, 12:52 PM
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Your question is the entire reason for my post. I wanted folks to think about what's happening in the pump, when it moves the needle of a "vacuum gauge".

So thanks for posting your question!

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Old 03-24-2023, 01:13 PM
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Quote:
Originally Posted by Schurkey View Post
Your question is the entire reason for my post. I wanted folks to think about what's happening in the pump, when it moves the needle of a "vacuum gauge".

So thanks for posting your question!
I truly appreciate another person trying to bring sanity to this discussion and physics! I admit that I tend to be overly sarcastic. Some tend to be overly sensitive. I bet at least one sent a PM to admin asking for me to be banned. LOL!

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Old 03-24-2023, 03:15 PM
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Quote:
Originally Posted by JSchmitz View Post
I truly appreciate another person trying to bring sanity to this discussion and physics! I admit that I tend to be overly sarcastic. Some tend to be overly sensitive. I bet at least one sent a PM to admin asking for me to be banned. LOL!
AND YOU WOULD BE WRONG, AS USUAL.

DID NOT HAPPEN. SPREADING FALSEHOODS AGAIN I SEE. TYPICAL.

Get real guy, it is a mechanical fuel pump discussion not a kindergarten playground.

Tom V.

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Old 03-24-2023, 04:07 PM
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Quote:
Originally Posted by Tom Vaught View Post
AND YOU WOULD BE WRONG, AS USUAL.

DID NOT HAPPEN. SPREADING FALSEHOODS AGAIN I SEE. TYPICAL.

Get real guy, it is a mechanical fuel pump discussion not a kindergarten playground.

Tom V.
Just speculation friend. Lighten up. Guilty conscience botherin ya? Otherwise, why so defensive? More children, in kindergarten, understand the fuel pump concepts than here! LMAO!!! They probably know what quotation marks are too! BWAHAHA!!!

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Old 03-24-2023, 05:18 PM
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when the mechanical fuel pump quits sucking the engine quits running, atmosphere same same

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Old 03-24-2023, 05:27 PM
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It also occurred to me that there’s atmospheric pressure on the bottom of the diaphragm via the fuel tank and atmospheric pressure on the top of the diaphragm. Therefore net zero motive force to fill the fuel pump. All of the suction or vacuum is created by the action of the pump.

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  #38  
Old 03-24-2023, 06:52 PM
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Do not be embarrassed, it takes some people longer than others to understand how stuff works.

Simple physics. Course, some have never had that class.

Tom V.

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Old 03-24-2023, 08:09 PM
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Tom,

I personally don't think anyone on this thread fails to understand how a mechanical pump works.... just maybe views it differently.

And I don't remember physics being simple.. but that's just me!

I do appreciate all the perspectives, knowledge, and experience... even if they come with a dose of caca, but I can choose to not read or ignore anything I want!

I find bouncing stuff off others is valuable, even if I step in it or worse, upset people. I may think I know stuff, and I may actually know stuff, but more often than not, I'm missing something or really don't know what I thought I knew... not physics, more like philosophy, but that was a different course and I did better in physics.

Mike

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Old 03-24-2023, 08:39 PM
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Thank You Mike for the nice note.

The thing I notice is the same person/people tend to stir the chit because basic posting
of valid proven engineering information seems to bother/bore them.

They want to make the posts entertaining and yet rarely is engineering "entertaining",
just hard work in college/university classes. As you know you can't change the physics.

But some can rarely post why and how engineering principals work.
So you get into the Opinions in the posts. My old boss said many times: "10,000
opinions is not worth one fact. But everyone has a right to post their opinions on a forum (even this one).

I am sure there are other Engineers out there besides Keith Seymore, (GM Engineering
42+ years, and I (Ford 39.5 years) Doing the job. Eric is an Engineer and I am sure
out of the whole PY population there are a lot more Engineers out there.

I have known a lot of Engineers who were not "Hardware People". Management Guys
who did an important job but not hardware guys.

But I am not envious of them. Everyone has a job to do.

Finally I see a lot of bored people on the board who just like to stir the chit for entertainment value.

Who would have ever thought that you could have a thread with people arguing how
and why the fuel flowed thru the gas line to the engine.

I personally have not run a mechanical fuel pump on my engines for 30 years.

I KNOW how my 450 Liter per hour EFI fuel pump feeds fuel to the engine.

PLUS these long posts improve my typing skills, LOL!

Just saying. Tom V.

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