Water pressure

[Stevan47]

Hi guys: is anyone out there able to tell me what the sea(raw) water pump discharge pressure is? The engine manual states 1,650 litres per hour (27.5 litres per minute) but how does that equate to PSI or mP? I am replacing the pump suction hose and as I am unable to source the original Premium Marine SAE J2006 Hardwall 100-0580 (5/8" ID) hose here in Australia, I need to know the discharge pressure so I can get the correct quality locally-manufacture hose. The pump is a Johnson, rubber impeller type. I imagine the discharge pressure would not be that great, maybe 20-30 PSI (?). Your collective thoughts/advice please, if you would. Kind regards

 

[lone ranger]

I doubt it's that high,your average car motor is more like 12-15 lbs.

 

[stwendl]

Well if you really want to know then look put this site https://www.physicsforums.com/threads/r ... re.615451/ referencing Hagen-Poiseuille assuming the end pressure is about atmospheric, you can then determine the pressure at the pump end and the hose pressure, if rated at that pressure and temperature, would be fine.


But like the other poster said, its not that high 🙂

 

[knotflying]

Your question is somewhat confusing. You are replacing the raw water intake? Is is it for the cooling or the wash down pump? On the intake side for either one I wouldn't necessarily worry about pressure. There is nothing on the intake side that closes that would develop pressure.

 

[lone ranger]

Hi guys: is anyone out there able to tell me what the sea(raw) water pump discharge pressure is? The engine manual states 1,650 litres per hour (27.5 litres per minute) but how does that equate to PSI or mP? I am replacing the pump suction hose and as I am unable to source the original Premium Marine SAE J2006 Hardwall 100-0580 (5/8" ID) hose here in Australia, I need to know the discharge pressure so I can get the correct quality locally-manufacture hose. The pump is a Johnson, rubber impeller type. I imagine the discharge pressure would not be that great, maybe 20-30 PSI (?). Your collective thoughts/advice please, if you would. Kind regards

Check your coolant tank cap ,it should have the pressure stamped on it.

 

[Stevan47]

Thanks 'loneranger': agree re the car engine comparison - that makes sense. I should have thought of that. Also, as you would know, the coolant tank cap relates only to the inhibitor coolant (under closed pressure) which is of course separate to the raw/sea water system that discharges overboard, so that will not really help me too much. In any case, good advice. Many thanks.

Thanks also to 'knotflying': Once again, I agree with you wrt minimal pressure concerns. The hose I want to replace is on the suction side of the pump and f'rd of the fine mesh strainer. As it is the original hose (100 category, premium hardwall) I want to use the same material if possible, just to keep things sweet. Blame my pedanticism/irrational attention to detail on the many years spent as a Navy Marine Technician: just can't shake the habit!

Finally, thanks to 'stwendl': appreciate your input. Will check out the website.

Kind regards to all

 

[SGIDAVE]

Hi guys: is anyone out there able to tell me what the sea(raw) water pump discharge pressure is? The engine manual states 1,650 litres per hour (27.5 litres per minute) but how does that equate to PSI or mP? I am replacing the pump suction hose and as I am unable to source the original Premium Marine SAE J2006 Hardwall 100-0580 (5/8" ID) hose here in Australia, I need to know the discharge pressure so I can get the correct quality locally-manufacture hose. The pump is a Johnson, rubber impeller type. I imagine the discharge pressure would not be that great, maybe 20-30 PSI (?). Your collective thoughts/advice please, if you would. Kind regards

Hello Stevan,

As you state in your initial post...the "pressure" in the section of hose between the raw water intake in the hull and the raw water pump is SUBatmospheric (i.e., "suction" or "negative" pressure). Pressure rating of the hose is irrelevant.

As others have responded, the remainder of the raw water circuit is relatively LOW pressure. The "discharge pressure" you ask about...hmmm, the raw water is DISCHARGED into the exhaust...no real pressure there but then the 'hose' gets significantly larger in diameter too. Again, it's "exhaust" rated hose; not an actual pressure rating.

This is what I used to replace a section of my raw water hose when I upgraded the raw water strainer. Go ahead and upgrade your stainless hose band clamps with the AWAB type while you are at it. Cheaper by the 'box'!

Good luck with sourcing proper hose,

dave

As I recall, my 21 EC has ¾" ID raw water hose. Use an "exhaust" rated hose of appropriate diameter with wire reinforcement. The wire is to keep it from collapsing whilst under increasing SUBatmospheric pressure as you increase the flow of the raw water pump (with increasing rpm).

 

[Stevan47]

Thanks for the good advice Dave. And yes, I realise that the suction side is negative pressure - I just wanted to use the same type of wire-reinforced hose to replace the original. Unfortunately, MPI is a US company so I am sourcing an identical material which is made locally. Just doing the research first. I will check out your arrangement. Thanks and regards

 

[knotflying]

Thanks for the good advice Dave. And yes, I realise that the suction side is negative pressure - I just wanted to use the same type of wire-reinforced hose to replace the original. Unfortunately, MPI is a US company so I am sourcing an identical material which is made locally. Just doing the research first. I will check out your arrangement. Thanks and regards

Just curious as to why you just can't purchase one in the USA and have it shipped?