Ducksta Posted May 16, 2004 Share Posted May 16, 2004 Heres my dilemma. If I siphon my tank with a short hose (1.2m) with a coke bottle on the end, it works like a perfect gravel vac, I love it. The water goes up 16" out of the tank and then down ~4' to the floor. The water flows hard and fast and dumps into the bucket at an extraordinary rate. When I dump water from my tanks with a 10-15m hose out onto the garden, it has a drop of about 3-4m the water seems to run alot slower, and cant be combined with a gravel vac. Now my question is, with the much higher drop, shouldnt the water run FASTER when I am dumping it outside? Link to comment Share on other sites More sharing options...
anchar Posted May 16, 2004 Share Posted May 16, 2004 Hi Ducksta, The amount of pressure "pushing"/"pulling" the water through the hose is dependent (in this case) on the length. The longer hose will always draw slower. If the longer hose had a greater diameter, then it would flow faster. merjo Link to comment Share on other sites More sharing options...
Chuckmeister Posted May 16, 2004 Share Posted May 16, 2004 Lol I'll have a shot at this one. I think whats happening is that the increase in drop will increase the pressure of the water flow but in the process will exceed what the hose can pump through it causing a backpressure. I think that the pressure is actually working against itself through the restriction of the hose causing a slower flow. Sorry a physicist I'm not or a plumber for that matter Link to comment Share on other sites More sharing options...
fiona Posted May 16, 2004 Share Posted May 16, 2004 Possibly the increased length gives increased turbulence (water would flow slower next to the hose itself, also more corners)?? 'Course I am no fluid mechanic. Link to comment Share on other sites More sharing options...
The Nightstalker Posted May 16, 2004 Share Posted May 16, 2004 I think i will have a go at this one to(did some physics at high school),now ,from what i remember, as gravity is the only thing "pulling' on it,the only difference will be the pressure of the water at the end of both hoses,they both should flow at almost the same rate,only the smaller diameter hose will have higher pressure due to the same amount of force acting on a smaller volume of water.I think........its been a while since i was at school(finished in 92,and at MT Druitt High no less)bye Link to comment Share on other sites More sharing options...
Tam Posted May 16, 2004 Share Posted May 16, 2004 its like friction and lubrication is it ? Link to comment Share on other sites More sharing options...
bishop Posted May 16, 2004 Share Posted May 16, 2004 My turn, The syphon effect is caused by the differnce in the air pressure on the surface of the main body of water (the head) and the vacumn cause by gravity drawing water down the hose. It is the same effect that allows a rotary water pump to work. Lower pressure on the inlet side of the pump draws water into the pump chamber where he impellor spins it to a speed where it is ejected on the outlet side (if this makes sense). In the case refered to the post the issue is with the difference between volumn and pressure. In general a greater drop with the same diameter hose will cause a high pressure (or suction). You have use a greater diameter hose so you have achieved a higher volumn at lower pressure. You will move more water but generate less suction. It is true that a longer hose will create more friction but this would be offset by the increased diameter (less friction per volumn). Does this make sense? Link to comment Share on other sites More sharing options...
Matthew Posted May 16, 2004 Share Posted May 16, 2004 G'day To solve your problem get a larger diameter pipe that takes the water outside. The two factors involved are the diameter of the pipe and the length of the pipe. Modify either of these factors and it will have effects on the flow of water. Thus shorten the hose and you will increase the water flow AND/OR shorten the hose. Incidently I saw it with my last water change: Two pipes had an identical 'drop'. However the most water was coming out of the pipe that had the smallest diameter. The reason: It was shorter. Sounds odd I know but try it yourself and you shall see. Link to comment Share on other sites More sharing options...
catcher Posted May 16, 2004 Share Posted May 16, 2004 G'day all, My turn, The basics are this, the fact that a coke bottle is being used is no more than a nice touch, It could have been anything with a large orifice! (nice marketing though, should be worth a case or two from coke). But, the longer the hose the greater the resistance on whatever is flowing through it. The best way I can explain it is that, it's the same with electricity, if you have small gauge wire supplying something that has a high current draw the wire heats up, I.E. diameter (gauge) is not great enough to supply the needs without friction. If you increase the wire (gauge) / size, the friction is removed because the area is increased and allows smooth flow. The same with fluid, the greater the diameter of the transfer piece (the suction hose) and / or shorter the distance, the quicker the fluid will pass through providing the pickup point is higher than the exit point. You can go into a lot of other crap explaining this but that's the basic's. Hope that makes it as clear as mud !!! Link to comment Share on other sites More sharing options...
Peter_Gun_Riff Posted May 16, 2004 Share Posted May 16, 2004 duck ur the one usually answering these questions lol Link to comment Share on other sites More sharing options...
Ducksta Posted May 16, 2004 Author Share Posted May 16, 2004 OK it is making sense to me. Thanks for the input. Except that everyone is commenting on hose diameter? It is the same hose - just in different lengths I think merjos suggestion I should use a wider hose confused some people? Link to comment Share on other sites More sharing options...
FREAQ Posted May 16, 2004 Share Posted May 16, 2004 My turn now. What I understand and remember fron high school physics which was 12 years ago, is that the larger diameter hose will flow more water than a samller one at the same pressure, so if you double diameter you quadruple flow at the same pressure, but using a longer hose of the same diameter (i.e. the smaller one)does increase friction which is caused by turbulance thus slowing down the water and getiing what is called back pressure. So if you want to drain you tank quicker get a bigger hose Link to comment Share on other sites More sharing options...
catcher Posted May 16, 2004 Share Posted May 16, 2004 Ok Duk, Long hose - slower flow because it has greater resistance. Shorter hose - less resistance, faster flow. Link to comment Share on other sites More sharing options...
Hoolig Posted May 16, 2004 Share Posted May 16, 2004 The longer the hose, water slows down, its called friction loss. Have seen this in practice when I was a Firefighter in UK, we were pumping water long distance in training for Nuclear War. Link to comment Share on other sites More sharing options...
anchar Posted May 16, 2004 Share Posted May 16, 2004 Hi Ducky, I think merjos suggestion I should use a wider hose confused some people? LOL...all I said was if your hose had a greater diameter, the water would flow faster.... merjo Link to comment Share on other sites More sharing options...
trofius Posted May 16, 2004 Share Posted May 16, 2004 ok I think there is an issue here that has been overlooked. the short hose 1.2m is falling 1.2m so it is an open end syphon, into a bucket etc (form the info supplied) the longr hose is 10-15m!!!! and has only got a 3-4m fall so 9-11m of this hose is lying flat, not hanging vertical.. So as well as the friction loss. in the hose itself the suction created by gravity is only working on 3-4 meters of this hose. and the weight of that 3-4m column of water also has to Push the weight of the other 9-11meters of water from the hose that is lying flat...( try this, fill the hose with water and try blowing it out the other end, while it is lying flat..) solution: cut the hose so that all that is practical is hanging and only a minimum is actually lying flat... Link to comment Share on other sites More sharing options...
Ducksta Posted May 17, 2004 Author Share Posted May 17, 2004 There is no part of the hose lying flat, it is taken out a window and along a wall at about a 20 degree angle and then splashing out onto a garden Link to comment Share on other sites More sharing options...
trofius Posted May 17, 2004 Share Posted May 17, 2004 really damm, well that was 10mins wasted last night then lol.... Link to comment Share on other sites More sharing options...
Ducksta Posted May 17, 2004 Author Share Posted May 17, 2004 Link to comment Share on other sites More sharing options...
Fixem Posted June 10, 2004 Share Posted June 10, 2004 I got something good out of this anyway. Made myself a syphon as described by Ducksta, but I used a No Frills bottle instead of a Coke one. Now the question is: Does a Coke Bottlle work better than a No Frills one? Link to comment Share on other sites More sharing options...
Cichlids_au Posted June 10, 2004 Share Posted June 10, 2004 Hydrodynamics, I love it. Your problem is indeed friction. Here we go (I have to use the word squared because I can't superscript the number) The Darcy equation states that the head loss hf (1ft head = 0.4321lbs/in squared, in a pipe of length, L, and diameter, D, is given by: hf = kf [L/D] V squared/2g where Kf is a friction factor, V is the water velocity in the pipe, and g is the acceleration of gravity = 32.174 ft/sec squared. Since the flow rate in the pipe is the product of the cross-sectional area of the pipe and the velocity. Cop that lot Link to comment Share on other sites More sharing options...
WAZ Posted June 10, 2004 Share Posted June 10, 2004 Hey Mark Craig Thompson will love that one He's the only one that will follow it too. rofl Warren Link to comment Share on other sites More sharing options...
anchar Posted June 10, 2004 Share Posted June 10, 2004 hf = kf [L/D] V squared/2g Smooth hose interior or ribbed merjo Link to comment Share on other sites More sharing options...
Cichlids_au Posted June 10, 2004 Share Posted June 10, 2004 I forgot to say that Kf is reduced by increasing the cross-sectional area. But Merjo said that already I'm working on Craig's problem atm but I've never used a bernoulli equation for a variable area flow rate to calculate water height at the weir Link to comment Share on other sites More sharing options...
Luke Posted June 10, 2004 Share Posted June 10, 2004 The Darcy equation states that the head loss hf (1ft head = 0.4321lbs/in squared, in a pipe of length, L, and diameter, D, is given by: hf = kf [L/D] V squared/2g where Kf is a friction factor, V is the water velocity in the pipe, and g is the acceleration of gravity = 32.174 ft/sec squared. Since the flow rate in the pipe is the product of the cross-sectional area of the pipe and the velocity. does that mean if I shorten my hose it will work better Link to comment Share on other sites More sharing options...
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