Water pressure spikes during porpoising

[Robbie Racer]

Have any of you other cat owners that have porpoising problems in smooth water and with bottom mounted through hull water pickups ever monitored your water pressure during the porpoise? Over the weekend I did some testing on San Luis with really smooth water conditions. My Carrera porpoised like it normally does between 70 and 90 and it popped the O-ring lid seals out of the two poorly designed WPM sea strainers. I have one through hull pick up for the motor and oil cooling and another for the innercooler. Both have separate WPM sea strainers with plastic tops with an O-ring to seal the lid. If the boat doesn't porpoise, I get a maximum of 30 psi on both at WOT. However during the porpoising, it spikes the pressure between 0 and 80 psi which blows the O-rings out and gets lots of water in the motor compartment. I'm thinking of installing two high pressure blow off valves that will open if the pressure exceeds 30 psi and dump overboard. Anybody else experience this problem? R/R

[Rexone]

The problem isn't all that uncommon. You need pressure relief valves off the strainer cans. you can likely just modify your existing WPM strainers by punching holes and welding some fittings in.
Our new strainers all come with a 3/4 NPT fitting now just for this purpose but most older strainers did not, including ours. The WPM strainers should be ok if you install the pressure bypasses and don't overpressurize them.
You do need to control the pressure though because you will have problems with engine gaskets too as they will not withstand that type of pressure spike for long, particularly the intakes. (Don't just install better strainers without solving the pressure spike problem.) Hope that helps.

[Robbie Racer]

Thanks Rexone for the reply. I agree with your suggestions and for the reasons you mentioned. Luckily, the WPM strainers do have an extra fitting welded into them already. That should make it easier to install the pressure relief valves. I found one design of a "calibrated pressure relief valve" that has 3/4" pipe fittings on the input and output and the pressure by-pass can be adjusted between 25-175 psi. I think maybe a setting of 30 psi should be a good start. I hope that size can dump enough water to drop the pressure to 30 psi during the spikes. Thanks again, R/R

[DogHouse]

You might want to look for a valve that will let you go lower. I run mine at 10 psi. I don't have a blower, but that amount of water keeps my 598 ice cold. I got my valve at McMaster-Carr.
-brian

[Robbie Racer]

DogHouse, thanks to the link. Which valve are you using? My motor builder wanted me to run at least 30 psi at WOT to make sure the motor was pressurized enough to eliminate any hot spots. R/R

[DogHouse]

I think I ended up with #7844K12, "Brass Adjustable Liquid Relief Valve 3/4" NPT Female". It's available in several different pressure ranges. Mine is 7-35psi. It's a big ugly brass thing but it works. McMaster doesn't have the best prices in the world, but they have a lot of hardware type stuff and their customer service and online shopping/ordering/tracking are excellent. I have mine T'd in to the inlet side of my oil cooler.
-brian

[Robbie Racer]

Brian, thanks for the info on the valve. It looks like it should do the job. I found a Wilkins Calibrated Pressure Relief valve here: http://www.zurn.com/pages/catalog.as...OperationID=11
It has a range from 25 psi to 175 psi and I think it's less expensive than the McMaster Carr valve. I will find out today when I try to pick it up on will call.
Thanks again,
Keith

[SVO 540]

Robbie Racer,
I have not noticed the spike in pressure you describe. I do have the exact same set up you have only I have IMCO sea strainers.
I force feed the innercooler with one of the bottom pick ups like you do. I do not have a gauge in my dash to display water psi in the innercooler. I was concerned about putting too much water psi to the innercooler so I hooked up a mechanical gauge directly to the innercooler. I wanted to have a maximum of 15psi at 100+ mph. I exceeded this so I put the boat on the trailer and ground down the pick up tube so less water would be forced up the pick up tube. I did this until I achieved my 15 psi goal.
Maybe you are forcing too much water into your sea strainers. Something to think about.
SVO 540 - OUT

[Robbie Racer]

SVO, I did the same thing you did by grinding the pick up to control the water pressure to the innercooler. BUT, I found out that if your boat porpoises, it may be spiking the pressure much higher than what it reads at a nice steady WOT run. I probably wouldn't have noticed either if it hadn't been for the poor seal of the lids on the WPM sea strainers. Good sea strainers have lids that are much more secure and probably would never blow a O-ring gasket out under any pressure you would see even in a pressure spike situation. As Rexone said, this can cause other problems down the road with water in the motor or possible a blown innercooler coil. If your boat never porpoises, then it won't be a problem. If your boat does porpoise, you might want to watch the pressure gage to see if it spikes higher than you want it to go. R/R

[gg10]

your engine builder wants to much pressure in the block,what you want is alot of volume through the block,not pressure.the volume will eliminate the air pockets.