Saturday, May 10, 2008

Water Waffle, redesign complete.

So the redesign is done bar the final welding.PRRT with its new hoses. 135 deg x 32mm and two 45deg x 32mm I/D.

If you want to neatly cut this stuff get some 32mm tube or the same I/D as the hose. Insert it, wrap some masking tape around at the cutting point. Cut around with a razor sharp knife using the masking tape line as a template. No nasty fluffy edges...Use a tiny bit of fairy liquid to get them on if tight...
All fits nicely. No stress on anything.
Ok thats the main bit done. Now the waffle.

With the EWP system or a normal system not the PRRT you could be quaranteed the swirl pot would flow outwards...However I read of some Caterham owners using the massive new bypass pipe as a heater return (to ensure all water goes via the PRRT (to quench any differentials before the engine = perfection (heater matrix cools fluid)...(bypass is the thing between the swirl pot and PRRT over the strut brace)...

This has made me paranoid about the pressure differential between depression and pressure and where this happens. As surely if these caterham owners are using the bypass as a place to return the heater water, then its either static (no flow pressure or not under a depression or suction from the pump (different to flow, I mean pressured flow, rammed or sucked...)...So its either niether suction or pressure and the Caterham owners are relying on the heater feed pipe pressure to blow coolant through the heater and its enough force to get it to return to the bypass or the bypass is under suction, or their heaters don't work?! System doesn't flow...Bypass could be pressured on the pump side, so the heater in and out are under pressure??...The heater is feed from the water rail, just before where my temp sender is, just after the kink out of the head. I will replicate the Caterham system.

Either their heaters as said rely on pressure from the water rail or the bypass is under mild suction or some combination of these factors or their heaters don't work well.

The heater is not my concern.

My concern is now having fitted the PRRT, the swirl pot MAY not be under constant pressure with coolant flow. So it may not always blow water out of the top outlet and into the airspace in the header tank. It would do with with the normal EWP or Thermostat, or with a remote thermostat as the radiator or small bypass acts as a restriction / centre of the system with the EWP alone and no stat. So the top hose is pressure, the bottom hose is suction.

They don't call it a "pressure relief stat" for nothing....It relieves pressure differentials also, flow pressure differentials...So it screws up my whole swirl pot plumbing.

I could bin the swirl pot...But I'd like to keep it as a 4 way union.

Same thing happens when you fit a remote stat in the top water hose, pressure and suction are placed on top and bottom hose...The small bypass creates a restriction so pressure will build up before the stat and small bypass, so swirl pot will flow out into a header tank with high pressure suction line in the base....

So in every situation bar the PRRT the swirl pot will act properly.

The swirl pot is the highest point of the system, which is not perfect as when the coolant contracts it will suck some air back into the pot as the swirl pot outlet/vent tube goes to air space in the header tanks and is above the water level...This will be immediately blow back out when you run the engine and any air quickly removed, alteast with EWP/EWP and remote stat, EWP and normal stat., stock pump and no stat, stock pump and normal stat, stock pump and remote stat. Under all these scenarios the swirl pot will be pressured and work fine.


With the PRRT (pressure relief remote thermostat) bypass being so big and used ALL the time bar when the engine is boiling 100C and the stat closes the bypass completely, there is NO assurance the swirl pot will not suck in air with the outlet line in airspace in the header tank.

I need to make some adjustments now.

The swirl pot outlet line must now go to below the water level in the header tank as its not assured the swirl pot is under pressure and may now flow out, and it will self prime, this way once primed it cannot suck air inward if the PRRT effects the differential this much.

I need to have a specific bleed and fill proceedure, where as before it would purge and prime the system even with the swirl pot above the coolant level in the header tank through its own action.

This is no longer the case (or may not be)...Worst case scenarios must be accounted for.

What will happen now is...

I will use the header tank to prime 95% of the water system. This will fill the head, rad and all pipes including the top hose....

However I cannot prime the very top of swirl pot as its above the water level. (problem generally this is, even with the header tank on the bulkhead.)

So I fill up the system up as much as possible with the header tank leaving the expansion space...Now I will stick the cap on the header tank, so it creates an enclosed atmosphere, remove the swirl pot outlet line and hold the feed line to the swirl pot (now taking off the header tank below the water level) upright so its higher than anything else.

I can then top of the swirl pot manually till full, the sealed header tank atmosphere will hold the added liquid in a hydraulic lock, so the water I am priming the swirl pot with cannot fall down and go back into the header tank cause its under its own atmosphere :) Once the swirl pot is full I will quickly duck the feed line to swirl pot downwards to below the level of the top of the swirl pot, till a little fluid comes out (bleeding the feed line)...Hold it up again and put the few drops of liquid back into the swirl pot to replace what dripped from the feed line...I then can replace/do up the swirl pot line.

Cause the swirl pot line is below the water level in the header tank and cap is on a hydraulic lock is created. I can then remove the header tank cap and like magic, the liquid that is above the level of the liquid in the header tank will stay inplace, the system is primed and under hydraulic/fluid lock...I can then run engine and sort out the final fluid level for the header tank.

I did some experiments yesterday evening on fluid dynamics and expansion. I calculated using my Alfa as a dummy that 8litres of coolant expanded to 8.3litres from ambient (16c) to 101c...

Each ML of liquid grew by 0.00040cc per degree of celcuis increase.

So basically there is not a fat lot of expansion happening. So I can run my header tank well over the level required to keep the head full. Also the Alfa test was done with the header tank cap off, so no pressure effect.

Thats important cause at the highest point of the head there is a outlet that goes to airspace in the header tank. However being as the coolant level in the tank will be well over the tapping on the engine, a hydraulic lock will keep all liquids in place. Also one could be concerned that during coolant contraction this line going to airspace could suck air into the head. However it will not as the tapping point on the engine will be below the coolant in the header at all times and there are 3 other lines going to the header tank all below liquid level, so when coolant contracts it will suck coolant from the header tank to replace it lost volume via contraction, not air, as air cannot purge back to this head tapping due to fluid level and fluid lock.

All quite simple, yet rather complex :)

Basically all this bullshit means:

The swirl pot with its outlet line below the level of the liquid (changed for PRRT) in the header tank will either do nothing under certain thermostat and bypass conditions and stay static, or flow outwards as intended and remove any air from the highest part of the system :) It cannot flow inwards, from the header to swirl pot cause where is the fluid going to go? The system is full and cannot force more water into the bled fluid lock.

So now there is nowt to worry about :)

Caterhams never use a swirl pot anyway, so I could just ditch it, as best it will work, at worst it won't do anything, either way its not really important...

Under fluid contraction after shutdown is the only time the liquid could flow backwards to the swirl pot, to replace volume lost in contraction :)

System has to bleed/fill in the manner above.

If you remove the header tank cap, no worries, liquid stays where it is, even though its above the header tank coolant level. However if you remove the header tank cap and take the connection off the swirl pot, the hydraulic lock is lost and air will rush in and allow the fluid that is normally locked over the header tank level in the top of the swirl pot to rush into and fill the header tank and be replaced by air... cause fluid lock is lost!

Simple physics.

Hope that helps ya understand cooling systems.

TVR use a similar system...The header tank is WELL below the engine and radiator, like 1 foot.

Proceedure for filling that is...

Fill the header tank to minimum line, place cap on.

The TVR has a swirl pot in the highest position on the system...So you then fill the cooling system via the swirl pot...Very much like mine, but mine is FAR less extreme...To get 100% fill on mine I need only add about 300ml of liquid into the very top of the swirl its near perfect with all the packing considerations its the best its gonna be. I have 100% faith in it.

So bar the heater/welding the new cooling arrangement is complete.

I should be able to fill the header tank 2/3rd's full cold. Well over the engine/head level and giving me 3x the expansion area needed from my test.

I can test the maximum the level by running the engine up 100C and topping it up leaving a bit of airspace in the tank.

I shall have the fan on at 90C anyways...

Happy with all that!

No comments: