What seacocks for GRP diesel tanks?

[demonboy]

I'm thinking of installing seacocks on my two GRP diesel tanks to feed the fuel line to the engine.

What type of seacock should I be considering? Are there materials in a normal DZR seacock that will disintegrate or corrode when constantly in touch with diesel? I'm guessing bronze would be ok but what about the gaskets inside the ball-valve?

How should I install the skin fitting? Is 5200 impervious to diesel or would I just be better to epoxy/fibreglass the thing in place?

Any thoughts greatly appreciated before I pull the remainder of my hair out :mad-new:

 

[Tranona]

Plain brass plumbing valves will be fine. There is no risk of corrosion as they are not exposed to an electrolyte and diesel will not affect them. not sure about sealing into grp. You will need access into the tank interior to put the skin fitting in so you will need to completely empty the tank and clean the mating surface. Outside should not be a problem with a sealant behind the locknut.

Having said all that, why do you want to do this at all? Presumably you have a take off for fuel already, so why not put an isolating valve in that pipe run if you want to isolate one tank, or have a crossover system so you can choose which tank to use.

 

[pvb]

If possible, tank connections should be on the top surface, with dip tubes as required. Very little chance of leakage then.

 

[MonniotC]

Big engine?

 

[sailorman]

I'm thinking of installing seacocks on my two GRP diesel tanks to feed the fuel line to the engine.

What type of seacock should I be considering? Are there materials in a normal DZR seacock that will disintegrate or corrode when constantly in touch with diesel? I'm guessing bronze would be ok but what about the gaskets inside the ball-valve?

How should I install the skin fitting? Is 5200 impervious to diesel or would I just be better to epoxy/fibreglass the thing in place?

Any thoughts greatly appreciated before I pull the remainder of my hair out :mad-new:

i have a gas cock in the 6mm pipe as it leaves the tank

 

[demonboy]

Having said all that, why do you want to do this at all? Presumably you have a take off for fuel already, so why not put an isolating valve in that pipe run if you want to isolate one tank, or have a crossover system so you can choose which tank to use.

Hi Tranona. Thanks for the reply. Normal seacocks it is then.

Just for posterity I'll explain our current set-up and why it's been a headache. Not looking for a solution to this because I'm going down the seacock route now, but...

We have a stainless pipe connecting the two tanks, around 2". At each end there's a right-angle elbow, which is welded to a steel plate, one for each tank. It's bolted on each corner of the plate through a threaded hole with nuts at the other end inside the tanks. Because of the irregular profile of the GRP tanks it was fitted with a nitrile gasket. Over time this disintegrated and one of the tanks started to leak. After emptying and cleaning the tanks we took the unit off, put in new gaskets, and put it back together. We fixed the original leak but introduced a new one. Tried another repair, which resulted in another leak. It was leaking through one of the bolts which was caused by ripping the threaded bolt hole. Retapped it, put it back together, but today it's now leaking like a sieve and we think this is because the stainless has bent so much it is no longer following the profile of the tank... or something. Also two more bolt holes appear to be shredded so we'll have to retap those. You can imagine how difficult, not to mention painful, it is trying to bolt this fitting on at eight points, evenly, one of us in the tank blindly scrabbling for the nuts, the other bent over with a socket set tightening each bolt etc etc.

We've now attempted this four times and just can't get it right. We've used nitrile, cork gasket, various gasket sealants and each time we put it back on we fill the tanks, find it leaks, drain it again... It's becoming increasingly frustrating, been going on for months and, because we're on the hard (again) we've had to move ashore because to do all of this we have to take apart the calorifier, which means losing water on the boat. Now we can't clean ourselves after getting covered in diesel each time so instead we spend the day swearing at each other, which does help in the short term but doesn't fix the leak. Fortunately the marina has cheap accommodation.

Actually we cover this whole issue in this week's episode, which we publish on Thursday, where we video our first attempt. Here's a screen grab showing the pipe bolted in place on one of the tanks.

TBH this is a silly design. We can't isolate the tanks with this system anyway (not that that's been an issue so far) and there is the potential for problems should there be any movement between the tanks, especially when hauling out. I do wonder if this connecting pipe was retro-fitted as our 435 tank configuration is different to most of the other 435s we've looked at.

Separate outlets from each tank via seacocks and hoses makes a lot more sense and it's encouraging to know we can use normal brass plumbing fittings. Thanks for listening!

 

[demonboy]

i have a gas cock in the 6mm pipe as it leaves the tank

Is it on the top of the tank, as suggested by pvb, or at the bottom like my connecting pipe?

 

[macd]

Big engine?

Not particularly: Oyster 435. Whatever it is, I doubt it needs to deliver more than the equiv of a small can of beer every four minutes. (I've been on board but can't recall the engine size.)

Demonboy: are there inspection covers on top of the tank? If so, you'd be best advised to follow pvb's advice and put the fittings through them, with a dip tube for the fuel outlet. A second dip tube on another fitting, to the very lowest point of the tank, will allow you to completely empty the tanks without major hassle.

 

[demonboy]

Big engine?

Beta 60. 6mm feed pipe but the connecting pipe between the tanks is around 2". That has a small cock on it leading to the 6mm fuel line.

 

[demonboy]

Not particularly: Oyster 435. Whatever it is, I doubt it needs to deliver more than the equiv of a small can of beer every four minutes. (I've been on board but can't recall the engine size.)

Demonboy: are there inspection covers on top of the tank? If so, you'd be best advised to follow pvb's advice and put the fittings through them, with a dip tube for the fuel outlet. A second dip tube on another fitting, to the very lowest point of the tank, will allow you to completely empty the tanks without major hassle.

Hey Mac. Yep, Beta 60 (we repowered a couple of years ago. When you came on board we had the old Perkins Prima).

We have inspection covers, conveniently placed at the back of the tanks, making it difficult but not impossible to reach the bolts of the feeder pipe! Of course I could just drill a new hole into the top of the tank.

The remaining issue is how I connect the two tanks when filling. That's partly what the current set-up is doing. I could glass over the current pipe...

 

[vyv_cox]

Our stainless tank has always had brass takeoff ball valve and plug, the former about an inch above the bottom. After about 30 years the threads in the drain plug corroded due to galvanic action in water lying at the bottom of the tank. Otherwise no problems at all.

 

[cmedsailor]

I'm thinking of installing seacocks on my two GRP diesel tanks to feed the fuel line to the engine.

What type of seacock should I be considering? Are there materials in a normal DZR seacock that will disintegrate or corrode when constantly in touch with diesel? I'm guessing bronze would be ok but what about the gaskets inside the ball-valve?

How should I install the skin fitting? Is 5200 impervious to diesel or would I just be better to epoxy/fibreglass the thing in place?

Any thoughts greatly appreciated before I pull the remainder of my hair out :mad-new:

Just a thought; fittings in diesel tanks (eg that lifting pipe, or just simple plugs at the bottom of the tanks) are either stainless steel or brass and are in contact with diesel permanently. So probably both SS and brass are fine.