Cold water is tapped off the pump, goes through a wound twine filter, in at the exhaust end of the heat exchanger and hot water comes out at the end closer to the engine.
This then goes into a reserve buffer tank. I have a drain valve at the top of the tank to let air bubbles out as i havent been able to eliminate them from the feed yet. I also have a bit of hose as pictured with a pinhole in it which should let the air bubbles out and only a very minimal amount of water should escape. This should also provide an exit path for steam. The buffer tank slows the rate the water temperature changes which gives me time to yank the hose if the temperature starts creeping up.
I also have a high temperature relief valve but the weld on threaded bungs havent arrived yet. Ill probably install one on the heat exchanger and one on the reserve tank.
I havent tested the unit in the field but running it off the cold water garden hose provides hot water and tepid exhaust (meaning its pretty efficient)
The craptiva EGR cooler was both cheap and straight, meaning it would be pretty simple for me to bolt another one in series and run the water through both.
Ive also wrapped the exhaust pipes all the way up to where the heat exchanger mounts on to keep the gas as hot as possible when it hits the exchanger.
not enough surface area and not enough BTU of thermal energy produced.S/Steel not known for its heat transfer either. I have just built a heat exchanger for a 6.5 hp engine and use a full 15meter length of 1/4 inch coiled copper tube and with the pump under a heavy load barely produced enough hot water to supply one diver let alone 2. the pressure of water supplied to the heat exchanger tested was between 20 and 45psi. Exhaust gases were stone could so every scrap of heat was extracted from the exhaust gases and the primary supply pipe from the engine was double lagged.
20psi seems high, but on a 6.5hp motor in cold water youre going to struggle as youre right, there is very little heat energy coming out of the exhaust.
Where ive seen people go wrong in the past is trying to have offshoots going into their boots and gloves and on the small motors there isnt enough heat energy to do that. I previously had a commercially made dredge hot water unit running on a 13hp honda and even then i struggled with getting water hot enough at high enough flow rate to be able to split off. I kept the water to a trickle, ran one line into my chest and was toasty warm.
It only takes a small amount of water coming into a well fitted suit to keep you warm while diving. The water i was operating in winter was 4°, the outside air fluctuated between -1 and +10
I think you may be surprised how much internal surface area the EGR cooler has, there is approx 5m of tube in there (24 tubes times roughly 20cm) did you test your unit to see if a shorter length of copper would do the same job? These units cost me $60 and the flanges pre made about 30 for a pair. Adding a second egr cooler id then have 10m of tube (appears to be roughly 8mm id tube, with a crimped pattern to increase surface area i imaging)
Im investigating making these commercially if theres any interest, i certainly have the motors here to test on haha. Ill let you know if i have success with the gx200
My system seems to differ from others. I’ve got the coil inside the original muffler.
Works great. Less complicated & easy to make. All mufflers have a seam around them. Prise it apart & coil as much 6mm copper as it will take. Just make sure the inlet end has a filter. Last thing you want is a block up in the coil.
If you want more heat out of your 6.5hps engine then it’s a simple job to rejet your carb to a bigger jet and stick on an open velocity stack air filter.
You will use a little more fuel but engine will run better. If you just rejet and use stock air filter it will run way to rich which is no good
Jet size to use on the Hondas would be a 0.85 to 0.90
KN open velocity stack air filters can be found online
Hi there been a while but retested my new heat exchanger after finding a faulty o ring in the flow adjuster. I always test my pumps/motors with 2 incn lay flat hose and wate rgoing thru a 20mm nozzle and a 40mm nozzle. This is regardless of the motor pump combo. The 6.5 HP motor was running at full throttle and against the 20mm nozzle produced 45PSI and filled a 44 gal drum in about 28 seconds. Run the test again against the 40mm nozzle and pressure dropped to 20 PSI but filled the 44 gal drum in 17 seconds. The hot water exiting at max flow was far to hot to put in a suit so I have had to make a mixer which I am not keen on but it has to be done. Have not run it to see what the change will make but its obvious the heat exchanger is working excellent. exhaust gas is stone cold exiting the heat exchanger so every ounce of heat has been extracted. So great result on a 6.5 horse motor.
On my big dredge I had a 15HP chonda with a custom made heat exchanger which was to alloy box section inserted inside the other with a water space only 2mm and the exhaust ran inside through directional baffles to extract all the energy out of the exhaust gases. This worked a treat and is as light as a feather. I have in excess of 3000 hours dredging logged over 3/4 years and ran the water from the bottom of the pump through a filter then thru a metering needle valve into the heat exchanger then into my wet suit. I never got cooked and if the heat gradually got hotter it was usually a part clogged filter. I had a 5 way manifold and ran external hoses to my booties and internal hoses to my gloves and 1 hose internal into my chest area. this system ran flawless for all those hours of use except for in the summer. the secret was creating holes to let the water out of the wet suit so back pressure did not let the water heat up by staying in the exchanger for longer periods. No steam traps or serge tanks needed.
The length in hose often dictates the temp on the smaller engines , if you have a 5 or 6 meter length of suction hose then make your hot water hose the same length, same with your air Line , zip tie the lot together .
I use 10mm airline for my hot water delivery with 1/2 inch foam pipe insulation wrapped in tape for the whole length from the reserve tank to about 1m from the diver. It has a lot of bouyancy but maintians the heat really well
