View Full Version : Pump Sucking Air ???
Avenger 1975
10-17-2005, 07:11 PM
Have patience with me guys, I'm learning slowly. '75 Avenger 18' with 455 and 12JC. I had a good run today, boat was running very well. Later in the afternoon I went out again and when I gave it some gas the boat barely accelerated, wouldn't even get onto plane, when I look back its not pushing much water. Engine is running fine. Is the pump sucking air from somewhere? At idle to 1500 rpm boat moves fine.
On my post from last week about the engine not idling, it must have been the moisture in the distributor, I aired it out for a few days and the problem is gone.
Thanks for any help on this.
you suck up some earth?? (grass??)
steelcomp
10-17-2005, 07:22 PM
Sounds like something in the pump. Maybe some earth. :D Sticks and stones, plants and leaves, or maybe a ski rope.
Squirtin Thunder
10-17-2005, 07:25 PM
Don't forget all the crap people drop in the water. I have seen some very strange thing in some pumps this year !!! Including baby diapers !!!
Sorry bout that brutha james! savanah made a mess and i was'nt about to drive the boat with that stench! lol
Avenger 1975
10-17-2005, 07:30 PM
We've had near flood conditions so lots of junk is floating around the lake, so maybe its something in the pump. I reached underneath and into the nozzle and found nothing, didn't pull the hand hole cover. Can you suck air through the packing gland? No water is coming out but I wondered if air can be sucked in.
if you crawl underneath the boat and look into the intake you will see the culprit!...then you will most likely have to pull the insp. cover!
if that is not the problem, you are asking the wrong cat!
Wicked Performance Boats
10-17-2005, 07:39 PM
With the boat out of the water, put your lips on the jet nozzle and blow real hard. Look under the boat and see if anything came out! If not repeat procedure till something falls onto ground. Budlight
thats one helluva way to sell boats! LOL not a bad idea though!
moneysucker
10-17-2005, 07:48 PM
With the boat out of the water, put your lips on the jet nozzle and blow real hard. Look under the boat and see if anything came out! If not repeat procedure till something falls onto ground. Budlight
Like him from hyperventalating from blowing into that thing for no reason.
It is not air. You sucked something up. You would be surprised how little debris it takes to do that. If you have a pop off make sure it is sealed correctly and completely closed, If you have an external clean out, (Which I doubt since you would have pulled it off to check since it would be easy.) make sure it is not drawing air from the clean out cover. It would be leaking inside if it was an internal clean out.
Cy
Wicked Performance Boats
10-17-2005, 07:50 PM
Sorry, I just couldn't resist the temptation. I apologize BL :D
BL, sorry bout that, did not mean to be that harsh! guess i should proof my shart!
Todd
Avenger 1975
10-17-2005, 08:01 PM
BL, I did what you suggested and a crumpled lottery ticket fell out, checked the numbers and its worth a million!
Its an internal cleanout and I didn't have time to pull the boat, will do so later this week and sounds like I'll find something inside. Thanks for the help.
Wicked Performance Boats
10-17-2005, 08:08 PM
BL, I did what you suggested and a crumpled lottery ticket fell out, checked the numbers and its worth a million!
Its an internal cleanout and I didn't have time to pull the boat, will do so later this week and sounds like I'll find something inside. Thanks for the help.
Dammit it! I always miss them big lotto tickets! Seriously though, make sure you take the boat out of the water before you remove the cleanout. If it's inside the boat, the boat will sink! BL
steelcomp
10-17-2005, 08:10 PM
Since a pump sees positive pressure on both sides of the impeller, how would it suck air from anywhere? :confused:
true and why does an imp. cavitate when the hull is clearly submerged under the water and no air is near??? does it pull it from the rear or the outside of the boat??? is there that much O2 in water?? not a physisyst so make it understandable! (please) lol
Todd
Squirtin Thunder
10-17-2005, 08:34 PM
true and why does an imp. cavitate when the hull is clearly submerged under the water and no air is near??? does it pull it from the rear or the outside of the boat??? is there that much O2 in water?? not a physisyst so make it understandable! (please) lol
Todd
Just to second Todd, how did my heart cavate when it is clearly submerged in bloode ???
Not good analagy but sort of the same thing.
Avenger 1975
10-17-2005, 08:44 PM
I mentioned it was rough on the lake today - when running downwind the boat came out of the water enough to cavitate the pump at times, I backed off the throttle as it would happen. The re-load on the pump has to put some serious stress on the impeller. Being new to jets I noticed it didn't seem to load up the engine like it does when a prop cavitates and then hooks up again.
Moneysucker, the guys got a 75' Avenger with a 455 olds and a JC pump. Chances are slim hes got a pop off. :D
moneysucker
10-17-2005, 08:59 PM
Moneysucker, the guys got a 75' Avenger with a 455 olds and a JC pump. Chances are slim hes got a pop off. :D
I throw out every possible scenario. I know a guy that pulled his bowl off on the sand bar to try to clean out what was causing the cavitation. turned out the gasket had folded and not seated right.
Just to second Todd, how did my heart cavate when it is clearly submerged in bloode ???
Not good analagy but sort of the same thing.
Glad to see you finally hooked up and regained your hole shot ther jim! lol
everyhing on the up-n-up??
Hope all is well!
Since a pump sees positive pressure on both sides of the impeller, how would it suck air from anywhere? :confused:
If you inserted say a 1/4" I.D. piece of tubing right through the side of the suction piece into the flow of water at a 45 deg. angle (angled so the opening of this tube is faceing the impeller) do you think it would be sucking air through that pipe or shooting water out?
The packings live in that type of situation, I personally think they will suck air if not sealed up well (even with 60lbs. of inlet press)If you ask guys like DPS, they crank down on the packing clamps after every run trying to get a good seal, which is why he came up with the seal pack which replaces the packings or rope seal.
Most all PWC have bilge pumps designed just like the tube in the suction piece example, and they work killer.
Anyways there is my 2 pennies.
maxwedge
10-18-2005, 09:11 AM
Have patience with me guys, I'm learning slowly. '75 Avenger 18' with 455 and 12JC. I had a good run today, boat was running very well. Later in the afternoon I went out again and when I gave it some gas the boat barely accelerated, wouldn't even get onto plane, when I look back its not pushing much water. Engine is running fine. Is the pump sucking air from somewhere? At idle to 1500 rpm boat moves fine.
On my post from last week about the engine not idling, it must have been the moisture in the distributor, I aired it out for a few days and the problem is gone.
Thanks for any help on this.
Hmmm... sounds a lot like rocks in the pump. Did you let my brother borrow it?
SmokinLowriderSS
10-18-2005, 02:23 PM
Late this summer, we had a serries of rainstorms. Drenched everything for close to 4 days solid. I went to a nearby lake the weekend afternoons after work and the debris was everywhere (the lake was about 10 feet above normal). On Sunday, idling away from the ramp, we must have picked up a small stick because on throttling up, there was a strange vibration and weak acceleration. 2 good stomps on the throttle and it cleared so had to be a piece of water-soaked wood that couldn't take 350HP.
Small stuff will cause cavitation spinning arround with the impeller.
Also, my Berk "F" external hand-hole cover will cause air seepage if the o-ring goes bad (mine did 2 years ago, it cracked & broke), I think the internal cover will too if it's seal fails but it SHOULD seep water stopped. My trouble wasn't really bad, but it was entirely noticable on acceleration, not so on top end.
sleekvino
10-18-2005, 03:37 PM
i had a plastic lid from someones salad get suck up in the pump felt like i broke something in the motor,i couldnt get it out in the water,when i got home i just put the hose in the pump flushed it out and was sitting on my grate.pulled it out problem solved. :crossx: :crossx: :crossx: :220v:
H2OT TIMES
10-18-2005, 08:27 PM
Sorry bout that brutha james! savanah made a mess and i was'nt about to drive the boat with that stench! lol
Ziplok bags work pretty good.
the ol' lefty works even better! lol
Mighty Thor
10-19-2005, 03:39 PM
Had mine plug up with river grass, stuff is about 6 feet long and it wraps around the shaft, then pulls loose from the bed of the river and feeds the free ends down through the impeller. First time it happned I was crushed, thought I destroyed my new used pump, after about the third time I started to catch on and would just reach through the hand hole and cut it out. That is how I lost my first two cheap pocket knives. They slip right through the rock grate and down to the bottom they go. Now I have a knife in the boat, tied to a lanyard with a key float. Love that River grass!
Rampager
10-20-2005, 06:24 AM
If it hasn't been said before the packing glands will definatly cause a pump to cavitate(suck air) under acceleration as this is a problem with the glands when they are not tight enough. Seen that very problem make for dramatic mass starts in river races when boats cannot get on plane
Cheers
I agree, thats what I was trying to get at in post #23, but nobody took the bait.
BUSBY
10-20-2005, 08:32 AM
75' Avenger with a 455 olds and a JC pump.
A 75' Avenger???? wow ... that's a long boat!
(Sorry Chris, couldn't resist ... we all knew you meant '75)
:D :D :D
steelcomp
10-20-2005, 05:20 PM
If it hasn't been said before the packing glands will definatly cause a pump to cavitate(suck air) under acceleration as this is a problem with the glands when they are not tight enough. Seen that very problem make for dramatic mass starts in river races when boats cannot get on plane
Cheers
So, on a DPS shaft seal, which way does the lip on the seal point?? To keep water out of the boat, or to keep air out of the pump?? I was always told to leave the packing loose enough for a little water to trickle through, that way the shaft was getting lubed. I don't recall having any cavitation problems. :confused:
Its a multiple seal piece,I think one seal goes one way, one the other way.Its all in a billet sleeve that presses into the bore where the packing normally go, the outside of the sleeve has o-rings.
Somebody on this board said something about it leaking alot of water into the boat and they were unhappy with it, I have not tried one.
Rampager
10-21-2005, 01:03 PM
I cannot answer your question as I am not familiar with that type of seal but I also would question both sides of the impeller being at positive pressure at low boat speeds. I belive there is a transition when boat movement starts pressurizing the suction housing. It wouldn't be called a suction housing for nothing! If you loosen the packing seal off till water comes into the boat when its sitting still that leak would likely stop when attempting to get on plane, assuming the boat did plane out but the pump would definatly be sucking air thru the packing.
Cheers
SmokinLowriderSS
10-21-2005, 04:29 PM
According to Berkley info I used to have, you should tihgten the packing enough to only admit a fine mist of water under high speed load. That way the packing is cooled at high shaft speeds. According to them, it should seal water-tight sitting still.
I cannot answer your question as I am not familiar with that type of seal but I also would question both sides of the impeller being at positive pressure at low boat speeds. I belive there is a transition when boat movement starts pressurizing the suction housing. It wouldn't be called a suction housing for nothing! If you loosen the packing seal off till water comes into the boat when its sitting still that leak would likely stop when attempting to get on plane, assuming the boat did plane out but the pump would definatly be sucking air thru the packing.
Cheers
I agree, we see that transition on our data systems.
I still think that when the pressure gets up to 50-60 lbs. in the suction piece its still sucking or pulling on those packings only because of the direction of water flow and the speed of the water going through the suction piece.
SmokinLowriderSS
10-22-2005, 03:01 PM
I agree, we see that transition on our data systems.
I still think that when the pressure gets up to 50-60 lbs. in the suction piece its still sucking or pulling on those packings only because of the direction of water flow and the speed of the water going through the suction piece.
I suspect that would be entirely possible, especially since the packing seal area is not smoothly in line with the fwd/upper face of the suction housing. It's little recessed area could easilly create a relatively low or negative pressure area at many boat speeds when the housing would otherwise be positively pressurized.
CrdStang
10-23-2005, 01:21 AM
Lets make a long thread out of this..someone explain the difference between 'cavitating' and 'sucking air'...
Here's a clue: Submarines, while hundreds of feet below the surface, can still cavitate the prop. Can't very well be air then, can it? Hmm....
SmokinLowriderSS
10-23-2005, 12:33 PM
Oh lord. Been working too many 12-hr days in a row to dig into my physics history. I'll leave this one for others, untill later at least.
Leav it at "anything that causes a suffuicient localized pressure drop to allow water to vaporize, even momentarally, causes "cavitation".
Alright, you forced me. :D
cav·i·ta·tion (kăv'*-tā'shən)
n.
1. The sudden formation and collapse of low-pressure bubbles in liquids by means of mechanical forces, such as those resulting from rotation of a marine propeller.
2. The pitting of a solid surface.
3. Medicine. The formation of cavities in a body tissue or an organ, especially those formed in the lung as a result of tuberculosis.
Rampager
10-23-2005, 02:11 PM
A sub prop can certainly cavitate as was hinted at in the above post.
If you really wanna twist your brain explian why those funky little contrails come off the tips of the wings of airplanes when they land(or when a fighter makes a tight turn) Is that the moisture in the air "boiling" due to low pressure???
Haha I get the idea this will open a can of worms! lol
Cheers
Wet Dream
10-23-2005, 02:59 PM
Actually, isnt it the moisture in the air becoming visible as it speeds up across the surface of the wing? Not the whole wing, but in areas where the air vortices, like off the tips of the wings? You are seeing a vapor trail as that air is cooled and condensed?
SmokinLowriderSS
10-23-2005, 04:47 PM
Actually, both of you are basically correct. The pressure difference at the wingtips causes vorexes (vortices) to form as air from below spills over into air on top, trying to equalize the pressure difference. If the conditions (air saturation) is just right, the moisture in the air condenses in this low-pressure turbulence to a visible size of droplet.
Check out some old pix (from WW2 is easy) of prop-drive aircraft at high altitude. In the right conditions, the propeler blade tips caused miles-long corkscrew-like contrails. The WW2 bomber pilots HATED this. Enemy pilots could literally spot them from 20 or 30 miles, FAR farther than they could ever spot a plane. Got more than a few of them killed unfortunately. Is a neat effect unless someone uses it against you. :eek:
Duane HTP
10-24-2005, 09:27 AM
I have a good picture of a graph from a run of one of our boats at Phoenix. It shows very clearly the amount of time that the pump is in suction and when it turns to pressure. If anyone wants to see it, email me and I'll send a copy. Or you can post it if you want.
Rampager
10-24-2005, 11:30 AM
Duane I would very much like to see that, perhaps posting would be easier for u if others want to see it too???
Cheers
Duane HTP
10-24-2005, 03:36 PM
Here You go. By the time I copied it out of Qwik Data and worked it over to show, it lost a lot of quality.
http://hi-techperformance.com/images/Suction_Time.jpg
You can see that the suction time was shortly after hitting the accelerator and only lasted about .7 seconds.
steelcomp
10-24-2005, 03:59 PM
What's really fun is seeing the contrails coming off the F1 car's wings on the race track. :DActually, both of you are basically correct. The pressure difference at the wingtips causes vorexes (vortices) to form as air from below spills over into air on top, trying to equalize the pressure difference. If the conditions (air saturation) is just right, the moisture in the air condenses in this low-pressure turbulence to a visible size of droplet.
Check out some old pix (from WW2 is easy) of prop-drive aircraft at high altitude. In the right conditions, the propeler blade tips caused miles-long corkscrew-like contrails. The WW2 bomber pilots HATED this. Enemy pilots could literally spot them from 20 or 30 miles, FAR farther than they could ever spot a plane. Got more than a few of them killed unfortunately. Is a neat effect unless someone uses it against you. :eek:
Wet Dream
10-24-2005, 06:57 PM
During recent flights to California and back, there is some interresting information I learned. These newer planes are awesome with fold down flat monitors for movies and FLIGHT DATA. That was the ticket right there. The ground spped you were travelling at, GPS location in the state, etc. But the thing that really got my interest, was the air temperature. At 37,000 feet, it was -52*F. 52* BELOW 0. Thats not including wind chill which is off the scale at 550 mph (ground speed). I know, planes relate speed to kts. While traveling at that temp, the windows on the plane would build up ice around the little pin holes that allow breathing. But knowing the outside temp was that cold, really put all of the pieces together while landing. The wings are frozen, but as you decend for a landing, the air becomes warmer and then you see the wings defrost. The condensated ice melts and you can see a whole lot of water now pouring from the wing and the flaps. It might even be that the plane is so cold and collects moisture (humidity) and runs off, but it was really cool to see.
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