D&G RO with broken shaft

[Brent]

So D&G are stonewalling me. They won't give me any kind of estimate for a new
shaft for the 150 GPH Airablo RO. They won't give me a price for a new pump. Just send
us your old pump and we'll rape you.

So, being in the machine tool business we use some high pressure pumps and the same people that make machine tool pumps Grunfos and knock offs, make stainless high pressure pumps.

I am thinking to get a 3 Hp 300 psi pump in it's simple form and the add a second pump for a recirculation
ciruit, maybe 1/2 or 3/4 Hp. The pressure on the recirculation pump is nothig special. The flow in would be just under 300 psi and the flow out would be a bit higher. I am thinking that I should get somewhat better overall performance because the re-cirulation would not be scavanged from the single high pressure pump that the system had originally.

We have the old pump torn down completely now and there is nothing, nada, zero, zip, at the bottom end of the 2' long shaft, which has 18 stages of booster impellers on it .... nothing to stabilize the bottom end.
Now wonder the danged shaft broken. This is one crappy design.

No wonder WMF reports he has seen "at least a dozen" with broken shafts.

D&G quality ???? If they have not improved on Airablo's design, well I wouldn't buy another.

Edit: and the shaft does not appear to be stailness. There is evidence of corrosion, likely cavitation cause, that has
reduced the shaft diameter by 10 to 15 thou. More at one end than the other, that makes me think the separation of some stages for recirculation and high pressure is a problem, causing the cavitation corrosion.

Edit 2: I guess you could say I feel like I'm getting shafted, or not getting the shaft or uh, whatever.

[Bucket Head]

Brent,
I'm sorry to hear that they are acting like that. I can't believe it. You would think that they would be happy to get you the repair parts, and that would keep their customers happy. This story is pretty bad public relations. Customer service is really a thing of the past with some people. Maybe you could try a Leader dealer? They are the same thing, just with a Springtech nameplate on it. Just thinking out loud here. Keep us posted on what you do. Your experience might help out other RO owners that have a failure with their pump.

Steve

[Brent]

Update on pump repairs

We dismantled the pump and found that the body of the pump housing, the stainless vessel
about 30" long and 5" diameter, is in fact a rolled and welded part. Inside there is a groove
the full length of the bore where the weld was not filled properly allowing high pressure sap
to leak into the re-circulation end of the pump.

Furthermore, the inside bore was not square to the pump mounting flange, causing the pump shaft
to be pointing off to one side of the housing and causing a stress flex on every revolution. And the poor shaft
that broke is only about 1/2" diameter. And furthermore there is no support bearing on the bottom end of the
shaft.
One member advised that he had seen a dozen of them with broken shafts. I'm not surprised.

We're honing out the grove and going to machine the motor mount flange so it's square to the honed bore
and we might get a bit better performance with a good seal, and hopefully never break the shaft again.

[Teuchtar]

Brent,
Good on-ya for reporting the root cause of the pump failures, and shame on D&G for not addressing this. Sounds like they have some generic weakness in the design and manufacturing process of that pump. If this was the automotive world we could expect to see a general recall for this product. I don't own such a pump, but as a turbomachinery guy, I strongly advise all owners to get in touch with D&G, have them describe their product recall plan. They should by-now have dozens of shafts of the improved design on order, and be able to tell us how they can turn around the upgraded pump. There's plenty of good machine shops around that can work to a sketch (or even your description) and tear down, remachine and rebuild that pump.
That once-per-rev flexing is called "high cycle fatigue". Normally 1045 steel would be said to have infinite life in simple HCF above 10 million cycles. At 3600 rpm that only takes 46 hrs. At 1800 rpm, 92 hrs. This means that the young pumps are at highest risk, and they would likely die in infancy. If they survive this infancy, the risk of failure later is much reduced ( well in theory, anyway). Thermal expansion effects will distort that simple answer, making it longer or shorter (all depending). But its true of all kinds of machines, if they don't fail in infancy, they can potentially live to a ripe old age.
You describe a 1/2" diameter at the break. Perhaps the shafts are missing the blending radius at the transition into that diameter ? Any increase (bigger radius) in that transition will help reduce the stress, provide the parts can still assemble together.
So, my advice is: young pumps are at highest risk. Old pumps maybe less so. But owners should make plans for upgrade.
Can't be much fun facing a bulk tank with 5000 gal of nice fresh sap, and no way to RO it.

[Brent]

This unit was made by Airablo years before D&G bought the business. Leader had many of them branded "Springtech".
My complaint was the months of back and forth with D&G with no willingness on their part to give me even an estimate
on the cost of repair, or indication that they understood the real problem, which they still may not understand unless
they follow us here or got the message through the Ontario D&G rep that I sent a report to. Their attitude was, we know what's
best and you should send it to you and we'll tell you how much it hurt before we send it back to you.
Just bend over and hold your breath.

By the way the replacement shaft that the Ontario rep finally got for me ..... still had the sharp corner with no blending radius.

The bad news is that the weld grove was worse than we thought. After honing 20 thou of material off, opening the ID 40 thou,
the groove is still quite deep. Perhaps still 10 to 20 thou deep. But now the walls are parallel and the taper is gone. There should
have been alarm bells going off when the guy that did the original assembly had so much trouble getting the O-rings and cup seals
in. They all showed signs of damage on original assembly. We're going to put it back together and test it in the next few
days. We'll see how it goes.

[Teuchtar]

Does taking the 0.020 off radius affect impellor tip clearance ? If so, you will have enourmous recirculation flow from impellor discharge back to intake, and pressure will be reduced. Pi*0.020*5 = 0.3 sq inches hole around every stage.

[Brent]

I'll post some pictures tonight that will show the construction of the pump to help explain. The clearance is not an issue

[Brent]

After I wrote all the the image uploader reversed the order.

OK I hope none of you ever have to see the guts of you pump so here are some pictures of ours.
The first is the pump dismantled laying on the grass. The motor is not there because the shaft broke.
You can see that about 2/3 of the way down the vessel there are a pair of ports for hose connections.
Below the vessel is the shaft with all the stages ( impellers ) on it. There is a cup seal about 2/3 of the
way down to separate the incoming sap at the top, from the high pressure sap below it. One port is
for the "built in" recirculation and the other goes to the "pinch" valve that controls the overall pressure.
Near the very bottom is another cup seal and corresponding port that goes out to the high pressure side
of the membranes.

The next picture is one of the impellers or stages. If you look closely you can see the circular vanes in the
thin section at the top. Each of these stages sucks in sap and expels it, raising the pressure about 12 to
15 psi. All of them raise the pressure to 300 psi. Each stage is open to take the output flow from the stage
above it. The impellers that are visible in this picture fit within the "cup" of the stage above it. This is where
the impeller clearance is set internally, not on the outside of the cup so the honing we did has no effect on
the clearance.

The last picture shows the terrible groove from the welding job on the vessel .... and this is after
taking 20 thou (20/1000") off each side, 40 thou off diameter. The groove is still 20 to 40 thou
deep. The cup seals that you see in the stack of stages are "supposed" to seal. There's no chance
that the cups will make a perfect seal, in my humble opinion. There has to be some leakage and
some loss of pressure. By the way the membrane tubes look about the same on the inside with a
groove where the lousy welding job was done.

If I get really inspired next year I'll pull it apart, fill the areas where the cup seals are supposed to seal
with weld, and then hone it again. BIG IF.

[Thad Blaisdell]

What a shabby job during manufacturing. D+G should have a general recal on all pumps and sue the manufacturer.

[Brent]

Please guys, D&G did not make this. It was made by Airablo before D&G bought the business.

I got really frustrated by the D&G correspondence about the repair.