Fitting sizes

[Baltimore Sailor]

I'm a bit confused about the fitting sizes at various points along the way from the pump to the manifold. The recommended hose size seems to be 1/2", as that's what the MMI store sells. However, the fittings at the pump and the thermostat are 3/8", while the ones on the manifold are 1/2".

Should I be using various bushings and adapters to ensure 1/2" barbs all along the way? What size are the barbs at the diverter? Or is it OK to put 1/2" hose on a 3/8" fitting where necessary because the clamp will seal it? It appears that the fittings Moyer sells are both sizes, but I want to make sure, so that I have max water flow throughout the system.

[Dave Neptune]

Baltimore, yes be consistant with the hoses. You can get 1/2" barb fittings with 3/8 & 1/2" NPT threaded ends. I suggest getting the right fitting instead of using adaptors which create more joints that could leak. I run 1/2" from the pump to the manifold. However I am running 5/8" from the manifold to the exhaust inlet on a raw water application.

Dave Neptune

[sastanley]

BS, Welcome to the world of figuring out NPT (National Pipe Thread) - which I was brand new to about 2 years ago.

It is a huge mess. 3/8" is not 3/8", & 1/2" is not 1/2". They are accepted "standards", that makes our lives miserable. Trying to mate these up with hose sizes that actually are 1/2" ID or 5/8" ID is sometimes challenging.

So, the short answer is, yes, and as Dave Neptune commented, you want to try to be consistent, but each additional fitting (or adapter) can add restriction. I think you want to be concerned that the hose barb diameter is correct for your hose size, and that it is mated to the NPT sized threads for the fitting your are screwing it into. Clamping a big hose on a smaller connector is not a solution..I've got some pictures to illustrate the results if you want to see them.

I ended up diagramming every fitting of my RWC system and then went to McMaster Carr and searched for each individual fitting...in most cases, they had what I needed if I was replacing it.

I'll give an example or two to see if it helps, starting at the water pump.
Here is how my Oberdorfer water pump is set up:

It accepts 3/8" NPT male fittings..The intake fitting is a 90 degree elbow with a 5/8" hose barb on one end (seacock to pump hose is 5/8"ID) & a 3/8" male NPT fitting on the other to screw into the pump. The output is a 3/8" NPT to 1/2" hose barb (a Moyer fitting I think.) - One additional thing you have to think about with two fittings close together is spinning them on so they don't interfere with each other either.

(this section edited!!) Moving up, the hole in the side plate is a 3/8" female NPT and likes the fancy 3/8" NPT male tee fitting from Moyer, but again, you still need 1/2" hose since the hose coming out of the pump and going to the t-stat are 1/2" ID & that's what the permanently attached barbs on the t-fitting want.

Up on the manifold, the holes are 1/2" NPT (female). I think the hose is still 1/2" ID coming out of the t-stat housing, so at the front of the manifold, you need a 1/2" NPT male fitting with a 1/2" hose barb (& a 90 degree bend!) At the back end of the manifold, the hole is 1/2" NPT, so you need a 1/2" NPT male fitting, but on that one the hose barb needs to be 5/8" since that section of the RWC system is 5/8" ID hose (like Dave Neptune's). I originally had a straight fitting here, but I am changing to a 90 degree elbow to better route the house under my cabinet that is in close proximity. At the same time, I do not want to introduce a restriction with a 90 deg bend, so I am trying to find a cast fitting, which seems to have much better flow than a hard bend fitting...this has been documented by Neil & Tom Thatcher over in Tom's FWC thread.

So, as you can see, it is a nightmare, it is unique to each boat, and I didn't even cover all the fittings. I found it best to methodically walk thru the system and take notes for each junction, and make list of their requirements (including if it might need a tee, male/female/elbow/45/90bend), then try to shop for the part(s). To top it all off, you may notice that some fittings have an extended neck on them that are custom made by Moyer due to clearance issues with the A-4, etc. (like the water pump or the side plate fitting.)

More fun with NPT...I had to use three fittings on my mech fuel pump (1/8" NPT by the way! ) to get the 1/4" barb to come out at the correct angle to avoid kinking the fuel hose and also to get the fitting to twist on around the various protrusions of the fuel pump. I used a 90 degree fitting that would screw into the pump and not whack the pump parts, then I had to add a stubby 45 angle to get the direction correct, and I could finally screw in the hose barb for the fuel hose..

Hopefully, I got all those correct.

[thatch]

Shawn,
You have far too much free time on your hands. Must be weather related.
Tom

[Baltimore Sailor]

The fittings on the diverter T aren't removable, are they? They didn't seem to be, when I was looking at them this weekend. Looked like a solid piece, like part number BRSS_05_219 in the catalog. (Parenthetically, that piece is labeled as a "reducing bushing" on the page -- that ain't right, is it?)

Can one measure the opening on the end of a fitting and get the correct diameter? Or is a 1/2" opening actually 7/16ths, or something like that?

[sastanley]

Tom, that was winter 2009 project...Now, I am doing it all over again as I prepare for FWC and moving up to 1/2" NPT and cast fittings wherever possible. It is often too cold to do any actual work, so documenting and planning and diagramming is all you can do. Sometimes it is so cold the graphite in the pencil freezes and it won't write on the paper...the ink in the pens all froze long ago.

BS, SOrry about that, I reviewed and went back and fixed some mistakes in the sideplate section after you corrected me in your post.. I know I have Moyer's tee there, now that you mention it. I had forgotten it was one solid piece. Hope I am not confusing the issue further.

part # OVWJ_09_219


edit - BS, our part numbers show the same picture...I got mine out of the Overhaul Parts -->Water Jacket section. Perhaps that "brass fitting" part number is mis-labeled or mis-pictured??

[Baltimore Sailor]

Not at all. Now I know for sure that they are 1/2" barbs.

[Administrator]

I got this from Don when I ran into the issue myself:

NPT dimensions relate to the ID of lead pipe which was used as early as the late 1800's to plumb homes. Since lead didn't have nearly the rupture strength of later materials, the wall thicknesses of lead pipe were very thick by today's standards, which made the OD of lead pipe quite large.

For whatever reason, convention has held to the approximate dimensions of the OD of lead pipe as NPT designations evolved and left the ID to increase as the strength of materials would allow for thinner wall thicknesses. Hence, 1/8" NPT pipe retains the original OD of lead pipe (approximately 5/16"), but the ID has been enlarged to approximately 1/4" depending on the strength of the material being used. In other words, nothing about 1/8" NPT pipe (or fittings) measures 1/8".

This same pattern continues throughout all the NPT sizes. You simply have to remember for example that 1/2" NPT pipe has an OD of approximately 7/8" and an ID of approximately .700".

To make matters much worse, the standard dimensions of "pipe" (as opposed to NPT pipe), "hose", "tubing", and "coil pipe" are all different and all require different fittings.

Bill

[sastanley]

Bill, I bet it is a simply fascinating event to sit across the kitchen table from Don Moyer and listen to him talk over a cup of coffee!

[Administrator]

Shawn, you have no idea...

Bill

[JonnyQuest]

After going over my cooling lines and seeing that they were in need of replacing, I noticed that the hose diameter from thermostat to the manifold is smaller than the hose used throughout the rest of the system. Is the smaller diameter hose here introducing unwanted restrictions on my cooling system, or is a smaller diameter hose intended to be used from t-stat housing to exhaust manifold?

I ask because I see in this thread that the consensus is that all the hose should be same sized.

Thanks for clarification.

PS- Thanks Baltimore Sailor, excellent questions here; helping me out as I work on my system!

[Dave Neptune]

JQ, no biggie. The bypass hose is the one many of us use a restriction in IE the bypass valve when not using a t'sat. As long as the hose is 3/8" HOSE you should have no problem. All this line does is allow a free path for the water to divert around the t'stat when it is closed to cool the exhaust and not restrict the pump.
Personally I would have far down on my to-do list changing it out to "match" the rest only so I would not have to keep two sizes of hose on board for extras.

Dave Neptune

[JonnyQuest]

Originally Posted by Dave Neptune

JQ, no biggie. The bypass hose is the one many of us use a restriction in IE the bypass valve when not using a t'sat. As long as the hose is 3/8" HOSE you should have no problem. All this line does is allow a free path for the water to divert around the t'stat when it is closed to cool the exhaust and not restrict the pump.
Personally I would have far down on my to-do list changing it out to "match" the rest only so I would not have to keep two sizes of hose on board for extras.

Dave Neptune

Hi Dave,
I wasn't clear enough in my wording, sorry. I am referring to the small 4" downstream hose that curves from the T-stat to the exhaust manifold, not the upstream bypass hose. Assuming the passageways internally are smaller than the 3/8" hose being used, I expect this isn't a problem either, correct?

[ndutton]

Some of us who have made the move to electric FWC posted pretty heavily about hose sizes and how we increased ours here and there to avoid restrictions and give our little pumps every opportunity to do their thing.

[Dave Neptune]

JQ, that short hose carries ALL of the water from the pump. I see you are in warm water so I would put changing to 1/2" on my list. If you have no heatiung problems you could slide it down the LIST.

Still no biggie.

Dave Neptune

[JonnyQuest]

Thanks Dave,
I still have a couple of more items on my cooling system maintenance, so I'll add teh new fittings to the shopping list.