Holding tank exhaust on a 1989 silverton

Hi,

You mght want to check your maths here F = P x A, if you change the value of either P or A the F number will also alter, if you had 250 psi at the outlet you would also have 250 psi at the tank top and wouldn't likely have a tank top still attached to the tank sides.

When pressure testing tanks it is well known that a 3m x 50mm tube full of water,exerts the same pressure on the tank top as a 3m x 100mm tube full of water.( mWc)

I didn't have a calculator handy so my math was in my head . The pressure /force that I was referring to would be at the surface of the drop tube, and minus any weight of the drop tube effluent column height. It seems that every time I make a comment or obsevation you (kiwi )feel obligated to correct me and its not just me you seem to lurk to jump on anyone who posts anything that you can argue about. In the real world , I tell people like you to blowme

That is some odd math.

I think there are better places to solicit such acts. But, putting your orientation aside for the moment, why would you want to become so intimate with someone you obviously don't like?

Hi,

I am sorry that you feel that somehow I have singled you out for some special correction, I had a quick look back at most of your previous posts here on YF to see where this was and did not see anything where I directly corrected or argued with your posts except here.

I also took a look at your public profile and was surprised to read that you say you are a Marine Engineer with 40 yrs experience who works as a consultant.

Someone who professes to be a Marine Engineer with that much experience and skill to now be called a Consultant should surely have some residual grey matter to keep the maths in his head company.

To get anywhere near 250 psi on your tank top you would have to have the effluent approx 550 ft up the vent line, that is some high mast (assuming your ventline goes up there)

If you are happy to give people you consult for mis leading information such as you posted here I feel sorry for your customers.

As for your closing statement, I am not that way inclined so you would not get the sort of response you expected should you say it to my face in the real world.

Hi,

That's a given.

This is what I wrote in post 21.

......if you had 250 psi at the outlet you would also have 250 psi at the tank top and wouldn't likely have a tank top still attached to the tank sides.

Numbers are very specific. Anybody who quotes them incorrectly and thinks it will not be challenged hasn't followed this forum closely enough. For some reason this weekend seems to be starting cranky. Must be a full moon.

250 Psi ??

Wow !! I can see you guys take no prisoners---So I'd better be careful here..

Maybe what our "250 guy" meant was similar to having 500 sq inches of surface area in an enclosed container, add 1/2 PSI to the enclosure, and then you would have about 250 lbs pressing evenly on all surfaces--But it's still 1/2 lb per square inch................???????????????????????????

Anyway, that's the basic princple to why a lift muffler can work so well and lift water up a smaller pipe with a minimum of pressure--It's trading a large surface area at low pressure for the velocity of the gases and water with the result being able to lift a water column much higher than the engine normally could without exceeding back pressure limits.. In a well designed lift muffler, it's typical to see 3/4 PSI lift water 3-4 ft ................Yes I know, a totally different subject but thought the analogy may help save our friend from being hung out to dry. ..

Tony

Thanks for the help sbmar, my reasoning is that I have used the application of low pressure air to pump 9 different gray ,holding and ballast tanks over the last 20 years thousands of times. I'll leave the math to the flightless bird and the small woodchuck. I'll bet that a 2psi positive air pressure on top of a tank thru the vent with a valve to control the inlet will discharge thru the drop pipe faster than a 2hp diaphram pump can pump it out.

I forgot to add that its the same princpal as a super soaker water toy

Be careful ... you are also confusing force with pressure.

If you have 3/4 psi you can lift seawater a little over 20 inches, the size of the pipe it's in is irrelevant, it could be 1mm or 10 meters in diameter, the pressure to lift it is the same.

What do you believe to be the back pressure limit for a marine diesel?

You're all wet mate. The pressure at the entrance to the nozzle of your water toy is the same as it is on the face of the piston. It is nearly zero as it exits the nozzle.

I suggest that if you refer to Mr. Bernoulli, at some point you will realize that the pressure across the nozzle must drop.

Hint: There is a difference between pressure and energy. There is a difference between pressure and force.

And I forgot to add, attempting to ridicule screen names doesn't increase your math skills or engineering knowledge.

Hi,

I read some of your posts on the other forum where you contribute all the time and are a moderator.

I thought you were pretty knowledgable but following the quoted text above wonder.

Posting junk like you just did really calls into question how much you actually understand about fluid and gas laws.

If you have 1/2" PSI per Sq Inch in the free space in your tank ( above the liquid level) that is all you have it is not 1/2" multiplied by the surface area of the tank top. I know fractions can be confusing ,This is why mWc is a much easier standard for people to understand.

Pressures

I think I may have not explained the point I was making properly... Yes, you still have 1/2" PSI (like I said) but 1/2" PSI acting on the the 500 sq inch surface area of the tank walls (or a piston if that makes it easier to understand what I was referring to) can lift 250 lbs, and on those 500 Sq inch walls, you have 250 Lbs of force spread out evenly try to push the wall out... That's all I was trying to say as maybe that's what are poster was referring to.....

As to exhaust pressure limits and diesel engines that was asked above-- Most manufacturers of realitively modern engines have maximum limits in the 1-2 psi range (20-60 inches of water column or 2-5 " Hg) .. These numbers are close enough for most preliminary exhaust design work..

Yes, you guys take no prisoners..

Tony

No, you have 1/2 pound per square inch spread out evenly. It's a tank, it has 1/2 psi on its surface and that won't change if that surface is round, square, 1 square inch or 1 square mile.

What you are saying is no different than stating that since atmospheric pressure is 14.7 psia there is almost 34 tons pushing down on a 4X8 sheet of plywood ... it sounds all techie and exciting but really means nothing.

The crap headed for the sky because it was accelerated by tank pressure through the nozzle formed by the pumpout connection.

I don't understand why it keeps flowing here.

Not when they keep charging the trenches, even if they are shooting blanks.

Pressure

Ok, you win, I loose.....................Obviously we have a language barrier, for sure we are on different frequencies, and we may even be on different planets............

Sorry I ever butted in..

Tony

Yes, you have to be on your toes with the tech guys, but deep inside they are * warm and fuzzy

* Not speaking from personal experience, attitude may vary pending current or past day/weeks events, amount of alcohol in the system, missed lunch or foul weather.