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15 hp vfd for 5 hp motor on compressor

Are the ones I have called disk valves?
Yes they are. Check the springs in them. Disassemble and lap the sealing surfaces on a surface plate, with some fine grit 400 wet/dry paper until they are smooth, with no wear grooves, using a circular 8 motion pattern to avoid going back and forth and being uneven. If you don't have a surface plate, use a glass plate and keep it lubed with water. If they are so worn that lapping cannot repair them, then they need replacing.

All pipe and tube connections should be air tight, I prefer sparingly using Teflon pipe dope over tape, to prevent loose shards of tape getting into the pump and valves, wipe away any excess outside of the connections.

Test the tank check valve for leakage of the disc seat by removing the pipe plug in it's side, when the tank has pressure in it. there should be no leaks if the disc is properly sealing. Be cautious when removing it under pressure, if it's not sealing properly the plug will want to blow out at you when you loosen it.


That LeROI Dresser model is getting up in age and parts can get pretty expensive when the demand is very slow.but leaving them leaky can be even more costly. The discharge valve on the second stage is the one to pay close attention to, as it is the most important, and see's the highest temperature use.
 
Ok.

I have three different grit diamond plates which I use to grind brazed carbide bits by hand. Always a mirror finish, especially with spit. :eek:
I also have silicon carbide paste #400.

The three disks take out so far. Numbering from left to right. 1 & 2 are from the 1st stage input. Number 3 is from the 2nd stage input.
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Number 3 looks worse in a picture. I looked at it under 50x and I couldn't see anything. Wonder if it's long term rust on stainless?
I soaked number 3 in phosphoric acid and it cleaned it up. But should they be so perfect to look as mirrors?
The reverse sides all look the same as untouched.

So I finally realized after all this is that the gradual fouling of the head valves over the years was finally exposed by a VFD failure.
I may not even need a new VFD. But should I be sorry? No. It's good to have a backup VFD or maybe two or three.
 
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Sounds to me like there could be leaky valves in the head or a leaking tank check valve, supplying tank back pressure to the pistons while starting under full tank pressure.

The fact that both VFD's do the same thing and it only happens when the tank is under full pressure, signify's that it is the leaking back pressure acting on the pistons during running. No leaking back pressure, no faults...when the tank has low pressure.

What type of valves does the pump have? reed or disc. Does the compressor have a check valve in the discharge line to the tank?

Normally you have two check valves in operation, one for tank pressure, and another set in the heads,
When the compressor was new to me there was a short 4' long 1/2" copper tube from the output of the 2nd stage to the tank check valve.
That short tube got replaced with a 50' long coil of 5/8" copper tubing. Can a length increase by 12x of the outlet tube make leaky valves more apparent?
It makes the unloading of air hiss for 30 sec when the pump stops.
 
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That short tube got replaced with a 50' long coil of 5/8" copper tubing. Much more back-up air reserve to fight the pump when there is a leak.
Sounds like your getting to the root of the mechanical problem, instead of trying to address it as an electrical problem. These type of valve problems are the demise of most single phase motors as well, making starting extra hard.

Valving is the first thing to check on a used piston compressor. Seen it many times when I used to service bump shop machines, For real busy shops. a continuous run unloader setup is best, similar to how a screw compressor operates. the last shop I rebuilt a 20HP unit for with a continuous run unloader lasted longer than the shop did.It was set up to be selectable for both modes of operation depending on how busy they were at the time.
 
Sounds like your getting to the root of the mechanical problem, instead of trying to address it as an electrical problem. These type of valve problems are the demise of most single phase motors as well, making starting extra hard.

Valving is the first thing to check on a used piston compressor. Seen it many times when I used to service bump shop machines, For real busy shops. a continuous run unloader setup is best, similar to how a screw compressor operates. the last shop I rebuilt a 20HP unit for with a continuous run unloader lasted longer than the shop did.It was set up to be selectable for both modes of operation depending on how busy they were at the time.
Yes, the single phase Baldor 5 Hp that came with the compressor smoked.
Since I parted the cases and painted everything grey I thought I might have caused the problem.
Anyway, the dealer replaced it with a single phase Weg 5 Hp. After 10 years of intermittent use the a capacitor in the motor box exploded and the motor smoked.
Then I switched to the Allen Bradley 7.5(5) Hp VFD with three phase 5 Hp motor. It worked for a while and then the faults. The rest starts at post #1.

I'm going to make a simple holding device for the valve pieces. They are .024 thick should be no problem to polish.
Another reason to keep bar cutoffs. I will show a picture of the tool later.

The those pieces are going to look like "fucking mirrors". Reminds of Spit-Shine Tommy.

 
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I am using what looks like a paper weight with a stub on the end to hold the valve. The stud is a turn down 3/8-16 bolt head. The height is 0.020.
The white sheet on the diamond stone is a ceramic piece. I use the diamond stone first and then the ceramic. I can use water or some final glaze.
The valve in front is the backside of number 1. Number 3 is on the paper weight reduced by .0005. The reflection is good enough to read a book.
But there are still fine scratches depending on the view angle. What do you think of the method and how far should I go with scratch removal?
Would you change the head gasket thickness from .040 to .065?

DSC_1670.JPG DSC_1673.JPG DSC_1672.JPG

If somebody wanted a fast fix, then just reverse every valve and install. It looks like I am the first one doing a op on these valves.
 
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what about the other half of the valve sealing surface and the spring?
Your only showing one of the sealing surfaces or half the valve.
 
what about the other half of the valve sealing surface and the spring?
Your only showing one of the sealing surfaces or half the valve.
That would be page 3 part #4 or #11.

The sealing surface in the assembly is recessed in the hole. There are two concentric ridges in the hole.
The height is not that much so there is a limit as to how much metal can be removed before there is no more height.
The valves in the pics show the concentric holes.

I thought about turning a round and attaching some 400 or 600 grit to it and swirl the round in the hole. But that would round over the ridges on both sides.
Or maybe just a sturdy round and some 400 grit carbide paste with some swirling action. I'm open to ideas.
 
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@rons We can't see what your working with, and an illustration in a parts manual just doesn't give the picture.

But to be clear both sides of the sealing surfaces need to be defect free if you want an air seal.
I'm not familiar with the pump style your working on, but if we could see what you see, we may have an idea. Most of your photos appear closely cropped on this end, and it would be helpful to se thee bigger picture.

A couple of older links that you may glean some info from by perusing with a sign up. I saw that one of the older poster links there had a manual for the pump you have, may be worth a try to see if you could reach him.


 
 
If you take a look post #118 2nd picture. All those plugs unscrew. The sealing surfaces are below grade.
There are two sealing surfaces which are two concentric raised rings. I was thinking cutting a piece of mystery
steel to fit into the hole with some carbide grinding paste.

Subject on rings. The top of the cover has a oil mist on it. Should I install piston rings? Just four bolts away.
 
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Here's my take on it, now that I got some time, and was able to study it for a few, it took me a bit to understand the functionality because the parts illustration and your photos are inverted from each other.

All of the other valve assemblies I've done previously were of a different design, they all had thru bolts holding the valve components together so they just dropped in as an assembly once lapped.

On the low pressure side (large) you have two intake and two exhaust.Valves.

On the high pressure (small) you have one intake and two discharge valves. The three intake valves, are currently the ones you have the disc plates and springs removed from. The other half of the 3 intake valves are still screwed into the head pockets.

On the low pressure side, it appears that one of the discharge valves has been replaced before, as it has a different casting design than the others. I would assume that the one with the radius slots is an original style, as the design is similar to the radius slots in the high pressure discharge valves.

To lap the concentric sealing ring surfaces of the intake valves, they would need to be unscrewed from the head, to do that properly. They may not need it as the intakes see lower temperature and pressure, only you could tell that by close inspection. But being that one has been replaced previously, likely means that they have seen a significant amount of service wear time and may need service.

The discharge valves, you have four, are the most important to be in good condition. Two on the low pressure side, and two on the high pressure. Take note that in the video you posted the two high pressure discharge valves are the ones that have been beat to pieces removing and installing them, these are the ones that are the most critical to sealing off the output and tank pressure, that leads to hard starts and your VFD complaining of over voltage and over-current.
Don't beat things up taking it apart, make a tool, clamp the head securely and use a pencil torch flame around the head casting vavve hole to expand it a bit. Keep the flame off of the valve insert plug as to not expand it, or ruin it;s temper. Patience is a virtue.

Get it all apart, perform a good close inspection, lap what you can, and try to buy what you need. If it was me, I would use a sparing amount of nickel anti seize when screwing those valve bodies back into their head pockets, and make sure you put new sealing washers under all of the valve inserts.

Pay close attention to the head gasket thickness selection, the parts manual says that with the wrong gasket thickness it's possible for the pistons to hit the head with the wrong stack height.

I can see why other makers used a bolted together valve assembly. and make sure that you test that tank check valve for leaking back pressure as I advised earlier, even if you installed it new. Trust but verify. The Teflon seat in them can become melted or contaminated over time and start you problem all over again.

Hopefully you can source all of the parts you may need. Take time and patience to get it right the first time.One last thing about the oil residue, the crankcase vent is normally dumped back into the head to keep things clean, so it is not abnormal to see some residue in there, in my neck of the woods on old style equipment, I prefer non synthetic 30W oil for the old seals and splash lubrication machines.
 
Post #118. All valve assemblies are out. The second stage disks look better than the input side ones. Probably because they were replaced.
There is what looks like carbon fouling on the backsides of the disks which can be scratched off with a finger nail. Oil baked.

When polishing with water I use a mixture of Kool Mist so the metal doesn't rust.

A couple gaskets look like enlarged copper compression washers for spark plugs. Another two are flat copper washers. One was misaligned and messed up.

My tool is a 4" long 1" diameter steel bar with protrusions on each end, one side two and the other side has three. There is a hex head cut in the middle.
Wonder if the guy in the video would be interested in my tool. :drink:
 
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was that mangled copper sealing washer om the high side valves?

Now that you have it apart, and can see what you need, will be the hunt to find the proper parts. How about the valve insert bodies, can you lap them properly now that their out? how did their sealing surface rings look before you cleaned them up?

What about the head gasket thickness, was their multiples and did you check their thickness? show us what you got.
 
was that mangled copper sealing washer om the high side valves?
No, low side output. Notice the blow-by on the warped washer.
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Now that you have it apart, and can see what you need, will be the hunt to find the proper parts. How about the valve insert bodies, can you lap them properly now that their out? how did their sealing surface rings look before you cleaned them up?
The second stage outputs are the worst. Middle pic with lapped disks.
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What about the head gasket thickness, was their multiples and did you check their thickness? show us what you got.
The gasket is .040 thick.

1. Tool I made from a off cut. Removes two and three spoke valve assemblies.
DSC_1677.JPG

Post 118 picture. I don't see a reason to remove the three valve bodies (lower left, two upper right). I can lap the seals in place.

Need two compression washers not shown:
ID = 1.000
OD = 1.25
Thick = .065 (compressed)

Need two thin washers like shown:
ID = 1.24
OD = 1.443
Thick = .020
 
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Hitachi WJ-C1 auto tune operation does operate different in Basic and Extended mode.
The stationary test in Basic mode vibrates the motor so much I rushed to press the STOP button on the first run.
The same test in Extended mode is much quieter. And the motor constants are different.

The observation here is that resistance and current goes up when a auto-tune is repeated with Extended mode.
In Basic mode the numbers are constant. I did a load default parameters in Basic mode and the H02X numbers are different
which I understand to be defaults for Hitachi motors.

Basic mode run 1:
H020 - 0.490 ohms (primary resistance)
H021 - 0.352 ohms (secondary resistance)
H022 - 5.66 mH (leakage inductance)
H023 - 7.78 A (no load current)
H024 - 0.055 (moment of inertia)

Basic mode run 2, 3, 4.
all of H020 - H024 are same as above.

Extended mode run 1:
Hb110 - 0.3761 ohms (primary resistance)
Hb112 - 0.2066 ohms (secondary resistance)
Hb114 - 5.1632 mH (leakage inductance)
Hb116 - 6.88 A (no load current)
Hb118 - 0.0169 (moment of inertia)

Extended mode run 2:
Hb110 - 0.3772 ohms (primary resistance)
Hb112 - 0.2079 ohms (secondary resistance)
Hb114 - 5.1307 mH (leakage inductance)
Hb116 - 6.93 A (no load current)
Hb118 - 0.0169 (moment of inertia)
 
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The video in post #118 shows the guy striking the side of a valve assembly to unscrew it.

Here is my head which was treated the same way. Notice upper left plug (assembly) and the chiseled spokes.
This is the output of the second stage and feels the most stress in life.
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By operating on the metal there the surface can raise on the opposite side and make the plate not exactly lie flat in order to stop air flow.
I chiseled out high spots and in the pic. Later I will lap the edges off the two concentric circles. I cleaned up top sides of both valve
assemblies at the upper left. The far left one is show here. If you notice the center circle and the weird wear patterns at 4 & 10 o'clock.
I think the plate was wobbling around due to non-flat surface at the outer circle.
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I called panzittasales.com 800 number and asked to order some valve gaskets and a head gasket. He said the price difference between that
and a rebuild gasket was $15 more but had more spare parts. So I ordered the rebuild kit for $79 and thanked him for the heads up. :drink:
 
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Good ting you decided to pull them out instead of trying to lap them in place, I'm sure that now you see what a fallacy that would have been. Kind of like the last re-builder beating them out without a removal tool.
I
That makes it pretty clear where your back pressure source was coming from, causing issues.Did you ask them if the2nd stage valves were available and cost?

A fresh set of sealing washers, along with your tool, will also help in not having to beat the valves back in, in order to try and get a seal.
Hopefully your kit will come with a fresh set of springs.

And a reminder not to overlook testing that tank check valve for functionality.
 
I'm leaving three assembly bodies in place. Turning a round of steel with different diameters on each end.
Slap in some 400 grit carbide paste and giving a few twirls. Don't know how to do this otherwise.

With the four assembly bodies that are already out I will have the steel cylinder vertical and twirl the bodies on top like a pepper shaker.
If I was to remove the three in the pic it would only accomplish replacing the seal underneath. I also test how tight they are seated.
Very tight, so much that my tool would put a small notch on the spokes of the body.
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What is not apparent in all this. Instead of spending $350 or $850 on a total rebuild kit the existing valves/seats can be surfaced down a few tenths.
At the rate I used to remove metal it appears that routine maintenance can make a new head with minimum cost. But if you are in a hurry the spend
money on the kits. The prices above are medium and large rebuild kit prices.
 
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