Mycom WA oil pump

[RANGER1]

Have had a few failures on Mycom recip oil pumps lately.
Starts off OK then oil pressure drops away after a few weeks.
Find oil pump rotor mills into drive end housing approx 1 mm.
Compressor overhauled 6 months ago.

Anyone have any ideas , as all pressures & temps appear normal on this machine.



Thanks

[Magoo]

Hi Range1.
interesting problem, wear on the drive end of pump casing. Could be a restricted oil cooler coil before oil reg feeding into drive end of crankshaft, so pump has to generate huge oil pressures above what you are reading on gauge.
Just a thought. Magoo

[RANGER1]

We installed a gauge on cono filter drain plug connection & oil priming valve after oil cooler .
100 kpa drop cuno to outlet of oil cooler & a further 100 kpa drop from there to end of crank where oil pressure is normally read + adjusted.
Total 200 kpa pressure drop which sounds fair to me.

[Grizzly]

Hi Ranger.
I have sent you some details which may or may not help?
I had assumed you would already have such info.
According to the info I have the Nominal oil pressure should be 20 - 43psi, Delta p = OP + SP. Models WA, WB, WJ- Relevant?

Maggo obviously knows these machines, as do I suspect yourself
better than I.

I agree with both of you however.

Something is throwing the oil pump.
When it was rebuilt was the oil drain mods to the main bearing carried out?
(Just something I read within what I have sent you)
Good luck Grizzly

[RANGER1]

Grizzly , thanks but not sure on mods you suggest .
Have not seen private message from you yet , will keep an eye out .

Out of interest Mycom decided to make a new style oil pump for A&B machines apparently!
Measured end float clearance & found it to be 0.02 mm , sound a bit fine to me seeing as though its next to nothing .
Also as Magoo pointed out about high pressures from restriction or something .
Apprentice thoght he saw 2000kpa on cuno filter on one start , also a bit of a concern.

[Grizzly]

Hi Ranger.
Check your email, as listed in your details?
Grizzly

[josef]

Hi, just my idea. I had the same problem Sabroe SMC Mk4. The problem was in the bearing, oil pump, Mycom has two sliding bearings, there would be proper to ask Mycom their comment. Many may also cause axial tolerances. Hopefully it will be useful.
Josef.

[Magoo]

Hi Ranger1.
the 20 bar would be a worry, have you had the oil reg out.
magoo.

[RANGER1]

Magoo,
Yes have installed a new one before this problem & have re-checked , seems normal no jamming ,nice & free.
Mycom have a new style pump which have no previos experience .
Pump has more lobes as well as idler gear. Rotor a bit longer as well.
Will instal old spare pump & see what happens.

[Magoo]

Hi Ranger.
What were the mods to mains that Grizzly mentions.
I wonder if Mycom have opted for a higher flow rate with new pump design and mains mods.
magoo

[HAROLDMYCOM]

Dear Ranger,

These problems only started after the overhaul or did you already discovered some problems before with the oilpump ?

I'm not a service expert but if your apprentice thought he saw 2000 Kpa on one start up you should see it again next start-up, did you ? Also did you replace the complete oilpump at first overhaul or only the oil pressure regulating valve ? And did you dissasemble the oilpump during this overhaul ? Normally Mycom recommends not to open this part unless really necessairy, remounting it properly isn't that easy.

If you don't find the trouble please check with a Mycom service engineer,

[RANGER1]

Thanks Harold , work is in progress.
Do you know of standard end clearances in Mycom WA/AB oil pumps for reference?

[CanadianIce]

Hi Ranger1

We recently installed a new N8WA at a site and the oil pump ( new style ) failed in 3 weeks. The same damage as you describe. After two more failures we still haven't got an explanation from Mycom. Compressor end clearances are all fine.

C Ice

[Magoo]

Hi Ranger 1
interesting comment from C Ice. Sounds like a factory problem with new pumps and they have not got to the bottom of it yet.
What sort of oil are you using?

[RANGER1]

Hi Ranger1

We recently installed a new N8WA at a site and the oil pump ( new style ) failed in 3 weeks. The same damage as you describe. After two more failures we still haven't got an explanation from Mycom. Compressor end clearances are all fine.

C Ice

Thanks CanadianIce ,
Glad in a way that were the only ones with this problem .
Its also like they could have changed manufacturers as new pumps now have Nippon pump company on them !
I also tried to measure another Mycom B pump we have which has never run . Its approx 0.03mm end float?

[RANGER1]

Dear Ranger,

These problems only started after the overhaul or did you already discovered some problems before with the oilpump ?

I'm not a service expert but if your apprentice thought he saw 2000 Kpa on one start up you should see it again next start-up, did you ? Also did you replace the complete oilpump at first overhaul or only the oil pressure regulating valve ? And did you dissasemble the oilpump during this overhaul ? Normally Mycom recommends not to open this part unless really necessairy, remounting it properly isn't that easy.

If you don't find the trouble please check with a Mycom service engineer,

The 2000kpa dropped off as believe it damaged pump & oil pressure kept dropping until oil fail switch came into play .
Never pulled pumps apart before running as no reason too.
We will be sending pumps back to Mycom , but imagine they will suggest stained oil or oil temp to high .
Oil temps 54 deg C Mycom state I think 50 deg C which is impossible in our climate.

[RANGER1]

Hi Ranger 1
interesting comment from C Ice. Sounds like a factory problem with new pumps and they have not got to the bottom of it yet.
What sort of oil are you using?

Magoo we are using Suniso 4SA which is recommended by Mycom .
When we instal s/hand old style pump we will be monitoring very carefully. It has 0.005"(0.127mm)
which is probably a bit much.
Experience tells me it should be around 0.003" (0.07mm).

[RANGER1]

Hi Ranger.
What were the mods to mains that Grizzly mentions.
I wonder if Mycom have opted for a higher flow rate with new pump design and mains mods.
magoo

Magoo,
Checked with Mycom & they say its interchangable as I also suspected it was a high volume or low speed pump.

Grizzly's mods are for A series so not relevant .
The mods were about installing an oil bleed off top of shaft seal compartment back into sump.
This was relevant many years ago as some compressors continually dripped oil from shaft seal no matter what you did .

[Magoo]

Hi Ranger1
Does that mean they have pump options for different compressor selection speeds.
Now that you and C Ice have screwed several pumps. Are the originals available still.

[RANGER1]

Magoo,
Apparently new oil pump is just a standard oil pump but for whatever reason they have changed design slightly , or its a new pump supplier.

Mycom have always offered 2 types of pumps
1/ normal standard oil pump

2/ low speed oil pump for compressor spreeds below 750 rpm. These have bigger gears etc.

We have found an old type pump thats O.K , so will try that .
As far as the high oil pressure who knows as I have never had a reason to measure pressure drop etc on oil circuit, as they have never played up before now.
This compressor has been runing for 15yrs so its not as though its new like C Ice's.

[Magoo]

Hi Ranger1
very interesting stuff, keep us up-to-date with progress using the older pump.

[fullmatty]

Perhaps you should check the length of the bolts going into the oil pump. We have found them to be a hair too long. In some cases and has allowed the pump to move and sometimes leak but not always.

[RANGER1]

We could not resolve issue with genuine mycom pump.

Aftermaket pump no problem.

Machines direct drive 1440rpm with genuine pump have massive pressure drop through
pipewok up to 1500kpa believe it or not.

On a compound 6-2WA oil pressure at cuno filter is 1900kpa with normal oil pressure
at end of oil circuit.

Oil pump must be to big as they changed design approx 3 years ago.

[Magoo]

Hi Ranger1
thanks for the up date.

[CanadianIce]

Just a followup question for fullmatty, who mentioned about bolts being too long. If you mean the bolts securing the pump clearance head to the pump body, then yes I can see leakage past the gear assembly and possibly externally into the compressor body. This doesn't account for the gear grinding itself into the head of the pump. Have you guys determined a reason for this and a remedy?

Thanks
C Ice

[RANGER1]

I havn't tried it but have a new pump ready & installed a 0.005' shim between pump gear housing faces.

Because all old original type pumps from what I have seen have about 0.004" to 0.006" end clearance as oposed less than 0.001" in new pumps.
Thought a bit of internal bypass wouldn't hurt in this case.

[CanadianIce]

Hi Ranger1

I see your point. Perhaps the clearance is too tight. I may try this myself. I planned on measuring the clearance of a new pump but haven't had the opportunity since the first failures.

Thanks for the good information.

C Ice

[RANGER1]

C ice,
I think the clearances scrape through on lower machine speeds, but not at 1440rpm.

See if you can put a pressure gauge on cuno filter housing for interest. Ideally before &
after modification.

[CanadianIce]

Ranger1

The 8WA that we had problems with, is running at 1250rpm. As soon as I can get back to the site I will try the mod and the tests. May be awhile before I get there but I will post the results.

[RANGER1]

C ice,
Out of interest from my sources @1000rpm oil pressure 1350kpa at cuno & 300kpa at end of crank
with 35 C oil

[IceMan_4000]

What Fullymatty is trying to explain is the fact that the flange thickness on the pump is what has changed.

I spotted this on a pump that was having pressure issues when the pump was removed the o-ring was not flattened like you would normally expect. A lock washer or even a flat under the head of the bolt with give you the proper seal on the pump. if the pump does not seal against the o-ring you will not be able to produce oil pressure. when we installed washers under the head of the bolt we then got full o-ring crush and the oil pump produced full pressure.

this might help. keep us posted

[RANGER1]

What Fullymatty is trying to explain is the fact that the flange thickness on the pump is what has changed.

I spotted this on a pump that was having pressure issues when the pump was removed the o-ring was not flattened like you would normally expect. A lock washer or even a flat under the head of the bolt with give you the proper seal on the pump. if the pump does not seal against the o-ring you will not be able to produce oil pressure. when we installed washers under the head of the bolt we then got full o-ring crush and the oil pump produced full pressure.


this might help. keep us posted

IceMan,
If I understand you correctly & "0" ring was not crushed, would'nt the gasket under the flange leak as well.
I thought fullmatty was talking about cap screws bolting pump assy together.

Besides we have way to much pressure , so maybe we can take "0" ring out! seriously

[fullmatty]

After speaking with a technician here is what we have found...He mentioned that upon assembly it looks as though they are filling the inner gear rotor opening with oil. Normally not a bad thing but unfortunately what is happening is that the screw rotor is not seating correctly. It cannot compress the oil back out of the opening.
Therefore it rides high on the oil and causes milling into casing.

[RANGER1]

After speaking with a technician here is what we have found...He mentioned that upon assembly it looks as though they are filling the inner gear rotor opening with oil. Normally not a bad thing but unfortunately what is happening is that the screw rotor is not seating correctly. It cannot compress the oil back out of the opening.
Therefore it rides high on the oil and causes milling into casing.

Fullmatty,
Can't grasp what you are trying to say on this one?

There is also a blind bearing on non drive end or rotor,this could also be
pressurized by excess oil pressure ,driving rotor into drive end casing.

Some pumps have breather hole in blind bearing hole to eliminate thrust.
Some even drill hole all the way through oil pump gear as a breather.

Still does'nt help us end users though!

[rnlmt]

Hello all
I have simalar problems with a Mycom N62A
On my 4 th oil pump they are lasting from 100 to 3000 hrs
Wear pattern on the drive end
Has any body found a solution to the problem.
Does a 0.005 " shim work ,
or putting it in the compressor without filling with oil first ?
Greetings .

[RANGER1]

Hello all
I have simalar problems with a Mycom N62A
On my 4 th oil pump they are lasting from 100 to 3000 hrs
Wear pattern on the drive end
Has any body found a solution to the problem.
Does a 0.005 " shim work ,
or putting it in the compressor without filling with oil first ?
Greetings .

Hi rnlmt,

You can prime up pump & oil circuit with oil, makes no difference.

Is that what Mycom suggest?
I'd invite them to site with a new pump & instal it to their requirements.

I got a new pump out of them but havn't used it, as I know what will happen.
I've installed shim ,but thats as far as I got.

My quick fix was to buy an aftermarket oil pump from Iseco in Brisbane & all is well.
Make sure its a Samwah though.

Mycom don't seem to want to know about it, which may not help you or anyone of course.

I havn't tested 0.005" shim theory yet, but its worth a try.

[IceMan_4000]

IceMan,
If I understand you correctly & "0" ring was not crushed, would'nt the gasket under the flange leak as well.
I thought fullmatty was talking about cap screws bolting pump assy together.

Besides we have way to much pressure , so maybe we can take "0" ring out! seriously

If you have too much oil pressure can you not back off the oil pressure regulating valve or do you have this all the way open?

Did you change the speed of this compressor? if you had a low speed oil pump and sped the compressor up this would make sense.

[RANGER1]

If you have too much oil pressure can you not back off the oil pressure regulating valve or do you have this all the way open?

Did you change the speed of this compressor? if you had a low speed oil pump and sped the compressor up this would make sense.

Iceman,
I probably jumped in assuming rnlmt has the same problem as I did or have .

The speed of our 6-2WB is direct drive 1440 rpm & has run at that speed for 20 years!
Instal a new mycom oil pump & nothing but problems chewing out pump on drive end.

Instal gauge on bottom of cuno filter & pressure is through the roof ( nearly 2000 kpa above suction)

Instal old style pump & pressure is 650 kpa at cuno & 350 kpa at end of oil circuit, which I would say is normal. Also continue to run.

The pumps supplied by Mycom are not low speed but gears are different than they used to be, from 2007 I am told.

The end float in a new pump is ridiculously small & probably not enough clearance for an oil film, especially
under the very high pressures they pump at 1440rpm.


rnlmt , does any of this relate to you?

If you instal the shim, be very accurate cutting it & line up pump exact during reassembly.
Pump should turn over nice & smooth, use lots of oil.

[rnlmt]

Thanks Ranger for that reply,
Not filling it with oil was suggested by a previous writer.
Mycom said to fill it with oil They replaced oil pump so far
but normally their pumps last up to 10 years.
I'll have a go with the pump you suggest
Thanks again.
Regards

[RANGER1]

Thanks Ranger for that reply,
Not filling it with oil was suggested by a previous writer.
Mycom said to fill it with oil They replaced oil pump so far
but normally their pumps last up to 10 years.
I'll have a go with the pump you suggest
Thanks again.
Regards

rnlmt,
Keep us informed how things go.

You also obviously have to mop out sump & clean oil filters to give new pump a chance.

Because you have had a number of failures, I'd do the same again after running for several days.
Sometimes installing a magnet (magnet out of old Parker LLC switch is good) in sump gathers up those fine particles.

[rnlmt]

Hi ranger1/iceman
After installing a new pump the pressure at the end of the circuit could easy be adjusted to about 3 bar above suction, the pressure would then slowly drop away making adjustments with the regulating screw necessary until this couldn't be done anymore.
End clearance of the new pumps seem very small and the pumps are of a different design then the old ones.
I'll give the new pump(from ISECO a fair go ( new oil etc ) and let you know if how I get on
Hopefully it will take a while
Thanks for your replies

regards

[IceMan_4000]

Please let me know what you find out. a Factory code of the pump. this would be good info as well. I have alerted my Parts manager to this issue, and have asked him to look into it.

[RANGER1]

Iceman4000,
Old style pump on left & new on right.

Part number do not have with me, but its a standard pump NOT low speed.
If it is ,they are all labelled & stamped wrong.

I've had 2 low speed WB pumps, with arrows on the wrong way for direction so nothing surprises me.










450.jpg

[IceMan_4000]

Thank you Ranger

Just to confirm a few things.

The new pump is chewing into the cover the part you have above the shaft and gear assembly. Is this correct.

the only major measurement I have been able to find different from old to new is the thickness of the flange and the shaft. the pumps seem very close in size and length.



I think we are actually close to an answer on this one. I hope to update you soon. I am not sure what part of Canada "Canadian Ice" is from but we have not had any contact from our contractors about this pump issue until very recent. We are acting to eliminate this issue. The Mycom Recip oil pump has been long known for its incredible reliability, and this issue will be resolved.

We have a theory here in the Vancouver office of the possible causes, and when I confirm my SWAG I will update you all.



Iceman-4000

[Magoo]

Hi Iceman-4000.
thank you for picking up and addressing this problem, Ranger will be happy. I was surprised Mayekawa had not addressed issue and sent out service advise
But what is SWAG. an internal abbreviation within Mycom Nth America. I have several WA machines that I sevice.
From Rangers pics, is the problem with the 6 flutes on rotor of new pump the issue creating axial or radial loads, or the overall length and pressure between the shaft and crank slot.
cheers Magoo

[RANGER1]

IceMan 4000,
To answer your question the housing on right , top of picture is housing that gear is milling into
(rotor driven by crank).
1440rpm is the killer, but also lower speeds. On test bench in Mexico pressure at pump (cuno filter bottom plug).
was approx 1200kpa with 300kpa at end of oil circuit (verbal conversation with our rep, but thats as far as it went!).
Total end float is the big one for me or lack of it, but its interesting that they changed a perfect design!

Thanks for your interest in sorting this one out.

[IceMan_4000]

Oh Ranger how so many of us are wondering why the change to the best oil pump ever. There was a group of us talking the other day about how many WA's and WB's we had overhauled before we worked for Mycom. The question was asked in all your years how many oil pumps have you changed out. We were hard pressed to fill one hand and there was 4 of us in the conversation.

We think it is a very minor change but we have to prove it first before I can say anything.

I will keep you all posted and update you with solution as soon as I can

A SWAG = Silly Wild Ass Guess My first year Refrig teacher taught me that one.

[IceMan_4000]

Unofficial word

The difference is in the bearing used in the oil pump. the older model pump had a groove in the bearing for the oil and refrigerant to escape. The new pumps did not have this groove. this has now been changed so oil may travel freely from pump end.

[RANGER1]

Thanks Iceman,
So basically the blind hole on the non drive end gets pressure behind it driving it into drive end end housing, is that what you mean?
I was even considering drilling a hole in end of pump & running a 1/4" line back to sump.
A lot of other pumps have hole drilled all the way up centre of shaft for oil ciculation.

I'm still a bit puzzled by the massive pump pressure at the pump though which I think is the root cause.
This in turn causes symptom of even more excess pressure in blind hole of bearing.

Thaks again, will take your advice & give it a go.

[IceMan_4000]

exactly Ranger.

the oil and refrigerant are getting trapped behind the non drive end and hydrolic forcing the gear forward. We were looking at tapping a hole in the end of the pump but I do not know if there is enough meat there for that

the new shaft has a hole down the center