Pump Lift

[Bob Poff]

Planning on adding a Racor as a primary fuel fillter.

The Yanmar service manual says that the feed pump on the 3GM has a usable "Suction Head" of 0.8m / 31.5 in.

1. Once inserting the Racor, how much does any flow restriction within the filter reduce the usable lift height? If any real world difference?

2. Is the total lift of the run additive/subtractive? For example does :12" up from the pickup, down 6", then up 8" to the racor add up to 14" of total lift to that point? Or is the location of the pump relative to the end of the pickup what matters?

Yes, a bit esoteric maybe......

 

[RichH]

What is the Racor part number that you are contemplating?

Go to the www.parker.com/racor website and look for (search): "your part number" + "flow curves" or 'flow vs. ∆P".

What you are looking for is the 'flow performance curve' of the part number. The flow performance curve will be have the flow rate versus the operating differential pressure (in various units of pressure or vacuum). Find out the maximum engine fuel consumption at 'wide open throttle' (WOT) for YOUR engine and locate its resultant pressure drop FOR A **CLEAN** filter on the 'flow vs. ∆P' curve.
THEN, If yours is a 'vacuum operated system', most small boat systems are, DEDUCT approx. 2 psi (6" hg. vacuum) and see if the result in 'flow' (GPH) is GREATER than the WOT fuel consumption of your engine. You will/should be changing the filter cartridge when the differential pressure (read by the gage) is approx. 3" hg. HIGHER in vacuum than when reading the gage when the engine is at WOT and with a CLEAN/NEW filter.

 

[kloudie1]

Lift question.. the lift is the distance vertically from the top of the liquid level in the tank to the suction connection on the pump, assuming that the line is full of liquid.. If you are starting with an empty line, it would be the distance from the liquid level to the highest point of any loop (assuming a loop would be above the pump) before the pump inlet.. THEN you have to convert the friction loss of the flowing liquid in the tubing and the pressure loss in the filter to inches of pressure drop and add that to the vertical distance measurement.. If the pump can do around 30 inches of mercury (not specified?) , that is about a vacuum and could lift diesel more than 30 feet .. 30 inches of total lift of diesel is another thing entirely! I think on my boat, the lift required is very small and with the tank full, I think the pump is below the level of the diesel.. .. I wouldn’t think there is a problem but do check the Parker flow curves as Rich notes..

 

[Bob Poff]

Thanks guys that tells me what I need. And where to go.

Claude, the full/empty line was where I was getting confused in my thinking.
Once the line is filled it becomes a closed system and the later half of my #2 question is sort of true. Except for my error in thinking of suction at the pickup. Not at the liquid surface.

Yes that's 31.5" of diesel they're refering to.

On our boats Claude you're correct with a full tank the level is above the pump.
With a near empty tank we're probably close to even. (Guessing as I'm 80 miles from the boat trying to remember).

So in the end, my guess is that unless I mount the Racor in the cockpit, I should have sufficient lift.
But I'll still work through the graphs just for fun.

 

[Dan Johnson]

Bob...

Putting the Racor up in the cockpit may be just a bit too high, especially when you need to prime it after a change. I'd suggest per our discussion on my boat that you consider somewhere that's inside the engine compartment, not higher than the cockpit sole.

While your at it, install the Racor vacuum gage too. It's worth more than its price and the plumbing needed, by far!

 

[Ron20324]

I'm not sure what the conflict is. Seems to me most boats have a racor-type filter already, and seem to work fine. Go with the guage!

 

[Ron20324]

Hey Bob! Where's the manatee?

 

[Bob Poff]

Dan the in the cockpit comment is from the realm of Illustrata Illogicae Extravagantum.

I was trying to picture 30" above the pump in my mind, and it occured to me that would up at the level of the cockpit.

Acutally the filter will probably go on the left side of the access hole that I cut in the quarter berth bulkhead. On the back of the refrig box. Along with an electric priming pump. And a vacuum gauge.

The reason for the question originally was that I was thinking about how much latitude I had on the height of the filter. That, for some reason, brought the memory of calculating hose friction in fire school several decades ago. One thought lead to another......

Also thinking of putting in a couple of valves so that when I change this filter, I can just route the output of the filter to the fuel return line. Should allow a less mess prime/bleed of this filter. While not introducing air to the line headed off to the feed pump. And a primative polishing route too.

Ron,
This is a new install of a primary. Along with a bunch of other stuff.
I'm just being anal about it I guess.

I haven't actually seen the manatee. It appears to like Manny's marina more than ours. And for various reasons we haven't been out.

I'm going to stop thinking now.... it gets me into trouble and makes my brain hurt.

 

[kloudie1]

Laughing, Bob.. Excellent notes..
Your idea of routing the filter bleed to the return line is outstanding.. I bought a Racor but haven’t installed it yet and will use your idea for the bleed! Thanks. If I had an electric pump on, I could polish my fuel with that line open and pump running while at slip.. Kool
My primary fuel filter is the original Fram that came with the boat.. I can’t find the old water separating element (looked like stacked popsicle sticks forming a circle outside of a pleated paper element?) so I am using a Wix element.. seems to be working fine.

 

[Ron20324]

I'm going to stop thinking now.... it gets me into trouble and makes my brain hurt.

"When I works, I works HARD...
When sit, I sits loose...
And when I thinks... I falls asleep..."

 

[Dan Johnson]

My brain hurts from all this thinking...

somebody please draw me a picture (it's the engineer in me, Gov).

Bob, when you get around to finalizing the filter placement, be sure you can not only change the filter but use the manual prime pump built in in case the electrification fails. I found the in-line bulb primer I showed you works better than the Racor one and its position makes it a whole lot easier to use!

 

[Stu Jackson]

Engineer-speak correction required

...the full/empty line was where I was getting confused in my thinking...Once the line is filled it becomes a closed system and the later half of my #2 question is sort of true. Except for my error in thinking of suction at the pickup. Not at the liquid surface.

That's simply not true.

An open system is one that is open to the atmosphere, like the flush tank in your toilet bowl, or a cooling tower in an air conditioning system. [added: or your fuel system, too!]

A closed system is where the water recirculates inside a closed piping system, like the freshwater coolant in your boat or car engine.

Both have pumps and the pumps work.

The difference is NOT whether you fill them up or not.

and the difference is in calculating the head or pressure. Open systems include atmospheric pressure because it's pushing down on the "open" liquid while closed systems don't include the atmospheric pressure.

 

[kloudie1]

Minor mis-understanding, Stu.. We were talking about an open system but with unfilled suction line looping higher than the pump suction.. The pump has to be able to lift the liquid above the highest place in the loop, but once it fills, the ‘lift” then becomes essentially only the difference in the level of the pump suction and the open liquid level.. You are right about the closed system..

 

[Bob Poff]

Yes Stu, an incorrect statement. I originally had included "Except for the air pressure on the liquid surface." But took it out for a reason I can't remember.
While I had the concept, just couldn't put it into the right words.

Anyhow....

Dan, here's a drawing of what I'm talking about.
I found this valve that should work.
Figure that I should be able to mount them such that in "RUN" the handles are vertical.
In "RETURN" the handles would be horizontal.
Just a little visual clue.

And Claude, yes, using this for polishing was one part of my thinking.

>>->
I just noticed that I didn't show the secondary filter on the drawing.
Let not your heart be troubled. It's there in the real world.
<--<<

 

[Ron20324]

Is it possible to delete the valve in the return line and put another direct input into the tank instead?

 

[kloudie1]

Kool find on the valve, Bob.. It sure looks like the water tank selector valve !!
Should be great for your application. If I'd known Jamestown had 'em for that low price, I wouldn't have rebuilt my water tank selector!... well, I probably would have for a spare.. (complusions showing)

 

[Bob Poff]

Thanks Claude. Found that particular valve by poking around the net.
I noticed that resemblance.

Planning all this stuff is fun.
With all this planning, now I just need to be able to find time to do it all.

Ron, I'm not sure what you open up by applying pressure "backwards" on the return line.
So I'm going to put that valve in just in case.

Dunno if I'm being overcautious or not.

Thought about a passive Y with checkvalves. But didn't like the idea of a checkvalve sticking closed.
>>->
I just re-read your post Ron. You're right. A second return line would eliminate the need for the second valve. Good show. I didn't think of that.
<-<<
As you easily can see, I have more experience herding around electrons than in fluidics and engines.

 

[Ron20324]

I spent 38 years in telephone electronics myself. On a phone company pension, I need to find the cheap/easy/lazy way to do things. Glad to help out. Keep us posted.

 

[Dan Johnson]

Hey Ron...

still in telecom, dealing with VoIP and all the new ways to do the same old thing. Retirement still over the horizon, and the climate neees to improve first. This forum is one of the ways to find out how to stretch the boat budget.

 

[kloudie1]

Retirement is highly UNDER-Rated.. I have been out now for 19 months.. kinda scary watching the market crater earlier, but doing fine now.
Nice to be able to go and play on the boat during the week .. Not as many projects have been done as I anticipated but she's getting there..

The valve on the return line side is not strictly necessary, since the other valve will keep anything from going wonky.. but it does no harm and makes for a more positive isolation. If I remember correctly, the return line has no dip tube so if one of the valves did leak while the engine is running, air would be sucked into the lift pump..