Dab jetsmart composite booster pump.

google Grundfos MQ3-45 check valve for more sites

copy and paste
https://rainwaterequipment.com/non-return-valve-for-grundfos-mq-3-45-or-mq-3-35-booster-pump/

https://www.pumpproducts.com/grundfos-96526663-non-return-valve-for-mq-booster-pumps.html



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It is a random traveling, in the pool, cleaning unit.
It can either be driven by water flow without a booster pump, or by pressure, which would require an additional booster pump. This will be plumbed so that its intake comes off of the main pumps return line and then a dedicated discharge line to feed the in pool cleaning head.
There are different types designated by a 3 digit model number. x80 = needing a booster pump and x60 - no need of booster pump. These work off of the return lines coming back to pool from main pump. All of the in the pool return fittings will need to be dramatically reduced down except for one (1) where you feed the unit from.

Then there are suction style that plug into a skimmer or dedicated suction port. These will bring debris directly into the pump hair & lint pot basket and the finer stuff into the filter. Where the Pressure style cleaners have their own catch bag.

Another cool thing is they are equipped with a "Back Up Valve" this little doohickey will pick up the unit every 4-6 minutes and get out of any stuck predicament, like steps, ladders, corners, etc. and send it back on its way in a different part of the pool, pretty cool huh?

Good luck

Check this out:

No idea here this is not a car question and iam not a plumber but i did have a emersion heater years ago and the cold feed from a header tank in the loft went into the heater and their was two feeds one from the tank and one direct from the mains with a special non return valve in the main line feed --why it didnt just fill from the header tank i have no idea but from that i would say the feed for your heater would be much the same with a header tank in case the inlet supply froze up ? Sorry iam a car mechanic so i have no idea but the return inlet pipe would be my logical choice

Can try replacing fuel filter

Well it should start ok but i think you may have a problem with it drawing in air along the fuel line somewhere ,normally this is caused by a deterioration of the flexible fuel lines on top of the tank and into the injector pump ,another little tric i do when i have starting problems is to fit one way non return valves in the feed and the return pipes as close to the injector pump as i can get them .A diesel engine will not toleratre any ingress of air on the intake side of the fuel pump

usual problem ,valves in injector worn for the fuel pump.easy quick fix this one ,fit a non return valve in the inlet pipe,check flow direction on valve when fitting and evan better as well is another in the bleed off return pipe .valves available from a motor factor or a specialist garage like bosch or lucas ,cut pipe and fit the valve with a piece of rubber pipe to connect the valve in line.or listen to the people who want to milk the golden cow and have the whole injector pump overhauled .

sounds like you have water entering the bores.Due to a slight leak from the head gasket.

Typically a water pump or booster pump would be placed on the main water feed (this assumes this line feeds not only the main cold line but the hot water system too. I work heavily with booster systems and would ask for futher information. Is this system runing off of a pressure switch such as starting a lower pressure and will shut down at a higher pressure or is it a constant pressure system where as the pump is expected to slow down or speed up to met demands? Either way the system will require a pressure tank, the first method of running will require a larger tank. With regadrs to connection this could be sweat in (with copper) or the use of mechanical connections. A proper "spring loaded" check valve would be required too.
I hope this may have helped,
Tom

HAVE YOU CHECKED THE FUEL LINES WHERE THE FUEL PRIMING PUMP IS CONNECTED FOR ANY CHAFFING THEY ARE COMMON FOR CHAFFING BESIDE THE FUEL FILTER WHICH WOULD EXPLAIN WHY FUEL IS RETURNING TO FUEL TANK.

detergent non return valve stuck, allowing water to back feed into the chemical tank.
depends on what machine it is as to where the non return valve is.