Siphon knowledge

[Richard]

Anyone understand siphons and/or where to get non-return valves that will tolerate petrol?

Situation: petrol tank for my bike is shaped like an inverted 'U'. Very clever in that the fuel pump is in one side of the U and there is no connection between the bottom of the two halves.

Solution: construct a self-priming and self-purging siphon that sucks fuel from the isolated half of the tank into the pumped side. Such a thing was made by an American chap according to a US bulletin board that I came across. It seemed to be, basically 'Y' shaped with non-return valves at the top ends of the valve and some sort of non-return purge-valve in the tail of the Y. The whole thing goes upside down into the tank with the purge valve at the highest point.

Unfortunately the designer dissapeared from the BB some years ago and I've not had any success posting questions on the subject.

TIA

Richard

[Thomas Prufer]

'ere:

It's a) in German, b) a stainless steel non-return valve, c) 19 Euro. The theory is: You stick into on the end of a tube, dip the end with the valve in the tank, shake it up and down to prime the siphon and get the siphon started.

Don't know it'll work for you, but it is an non-return valve that will tolerate petrol...

Thomas Prufer

[Andrew Mawson]

sucks

OK my motorcycle knowledge is somewhat dated, but every tank I've been associated with 'hung' over the top frame rail, and had two outlet taps which fed pipes that came together in a 'Y'. This way you always had a 'reserve tank' when the level got down to the situation you are describing.

AWEM

[manatbandq]

I assume that is sarcasm. Are you sure? Why would the designers be so stupid as to fit a tank that can never be fully utilised?

MBQ

[The Natural Philosopher]

Well as you go round corners I expect it sloshes a bit anyway..

Or has an internal coupling between the two..

[manatbandq]

But no guarantee where it ends up.

That's what I suspect, or external as another poster implied,. The OP implies there's no connection and he is trying to fix the stupid design.

MBQ

[mike]

[e-mail] wrote in news: [e-mail]:

Maybe not, it all depends on the dimensions. My bike taps inlet ends used to be set up a bit from the bottom of the tank to help avoiding crud entering. If the cutout for the to tube ends up being quite shallow at the back end, then sloshing around plus the height of the petrol tap feed may make all practicable use of the petrol.

mike

[<me9]

I'm sure I had one at one time where the (one) tap had a main and reserve setting, with the main coming from an upstand into the tank.

[adder1969]

My BMW petrol tank is lik two saddle backs over the propshaft. I guess that the action of filling up the right hand side primes an internal pipe to the left hand side, then as the right hand side goes down the fuel flows from the life through this pipe. Or not.

[mike]

wrote in news:4E41B4EE97% [e-mail]:

My bike taps inlet ends

You certainly did - they were dead common.

The tap has two concentric inlets at two levels; when the higher inlet runs out, you change the tap to "reserve", and it allows perol to enter the lower inlet.

Al you had to do was remember which way to turn the tap when it happens when you're halfway through overtaking a juggernaut

mike

[Andy Dingley]

Simply link both sides with a U pipe. No valves or taps needed. Provided the pipe is big enough, then flow through this link pipe will drain both sides equally, leaving you with a trivially small undrainable volume that's merely the contents of the pipe.

But motorbikes generally tap both sides anyway, and have a changeover tap. This gives you a reserve available only by switching over which is the volume of one isolated side. Cleverly this reserve is also "automatic" and you'll still have a reserve next time, even if you forget to switch it back when you fill up.

[Richard]

Yep, all my previous bikes with saddle tanks were thus equipped. Not so the products from BMW or, at least, in the case of my R1150GS

Richard

[Richard]

Totally sarcasm free. You might care to examine the next R1150GS you get close to.

Richard

[Richard]

A bit

None. Hence the siphon solution. The desparate out-of-petrol solution is to lean the bike over towards the pump half.

Richard

[Richard]

The OP

Yep. It's a BMW.

Richard

[Richard]

Yep. On bikes with external fuel pumps or simply gravity fed carbs. Not so on my FI BMW.

Richard

[Richard]

Which BMW? My R1150GS has no link

>

[Richard]

I'll try it. But how will the fuel be drawn from the side without the pump over the top of the inverted 'U' into the side from which the fuel is pumped?

Not where there is an in-tank pump.

TA

Richard

[Guy King]

The message from Richard contains these words:

Sometimes the top tube slopes enough so that at the nuts end of the tank there's no bridge for the fuel to cross. My DT125 and CX500 were like that.

[Andy Dingley]

It won't - use a U pipe, not an inverted U.