O2 conversion on Sierra Booster

[tbone1004]

Alright all, and paging @Wookie as I think you've got experience with this.
I picked up a used Sierra booster because I have no self control.
I contacted Masterline who sent me the repair manual and a quote for about $1k for their "rebuild kit" which also includes some tools that I'm going to need to replace the seals.

Their part numbers for the o-rings all have 010 in them so hoping someone can confirm those sizes since they charge $5 each for them...

@rddvet any chance the next time you have the cover off of yours you could post a picture of the plumbing? I understand the Sierra's are single stage, double acting, and I'd obviously rather change this to two stage-single acting to slow the fill rates down and decrease the heat generated with big deltas of inlet/outlet pressure.

I already have a motor ordered to convert to 3p with a VFD which is good so it will be able to run off of a standard wall outlet, and other than that I don't think I have a whole lot else to deal with.

Not a lot of discussion on these and sine the Sierra's seem to come up for sale pretty inexpensively I figured I would do a full "conversion" thread since the parts are just under a grand which makes converting one of these pretty cost effective.

Thanks!

 

[Wookie]

Alright all, and paging @Wookie as I think you've got experience with this.
I picked up a used Sierra booster because I have no self control.
I contacted Masterline who sent me the repair manual and a quote for about $1k for their "rebuild kit" which also includes some tools that I'm going to need to replace the seals.

Their part numbers for the o-rings all have 010 in them so hoping someone can confirm those sizes since they charge $5 each for them...

@rddvet any chance the next time you have the cover off of yours you could post a picture of the plumbing? I understand the Sierra's are single stage, double acting, and I'd obviously rather change this to two stage-single acting to slow the fill rates down and decrease the heat generated with big deltas of inlet/outlet pressure.

I already have a motor ordered to convert to 3p with a VFD which is good so it will be able to run off of a standard wall outlet, and other than that I don't think I have a whole lot else to deal with.

Not a lot of discussion on these and sine the Sierra's seem to come up for sale pretty inexpensively I figured I would do a full "conversion" thread since the parts are just under a grand which makes converting one of these pretty cost effective.

Thanks!

I did not do the conversion, I bought the Masterline. I had the tools, but when I was able to double my money selling a Masterline with 400 hours on it, I threw in the tools. You are correct, the Sierra is single stage double acting and the Masterline was as well. I don't know if I'd make it a 2 stage single acting with 2 stages the same size, but if you have experience with that, it might allow you to scavenge down below 300 PSI He without burning anything up. Is Masterline selling you the conversion kit or the rebuild kit ($400 last time I bought one)? Also, I had a number of adiabatic flash fires in mine until I put a sintered filter in the inlet of the booster and the outlet of each stage. I bought them from Tony Land at Add Helium, they were removable and cleanable, and I was astounded at the amount of fuzz (looks like carpet fuzz when a new carpet is being laid) there was in bottled gas. Have fun, they are an amazing unit. Very fast, I used to scavenge ABO after a tech trip and store it in my owned O2 cylinders pretty quickly. At least fast enough that I wouldn't get bored. Be careful filling 2 and 3 liter cylinders. You can get them too hot to touch.

 

[Wookie]

And, o-rings are the biggest scam on the planet. My new boat has MAN engines in them, and the heat exchangers are o-ring sealed. MAN wants $240 each for 4 of one size, and $180 each for 4 of another to service 2 engines. The parts manual calls out the o-ring size (in metric) and the durometer and material, which I don't remember off the top of my head, but 10 of each size was about $10 including shipping from Amazon. A simple Buna-70 was getting upcharged $239.

 

[tbone1004]

@Wookie Masterline doesn't have a conversion kit, this is only the rebuild kit from them. This price includes like $200 in tools to do it properly and a $300 piston guide which says to replace every other seal change. Not knowing the full history of this thing I'd rather rebuild it all in one go.

I may leave it plumbed as is and use intermediate bottles, not a big deal to do it that way for me either. I'll be putting the VFD on to slow it WAY down for rebreather bottles and I do have Swagelok filters on my whips to keep the inlet gas clean.

I get the markup on o-rings to a couple bucks each since I'm sure they're doing some sort of inspection on them, but even if not, there is labor tied up in separating them as well as materials for the baggies/labels/handling/etc, but if they are 010's, then I'd rather buy a bunch of high duro one's *scuba 010's for the reg hoses are 75's for anyone not paying attention*, and call it a day.

 

[iain/hsm]

Can I offer some small pointers on this suitability for Oxygen with these boosters.
To kick off these oxygen builds were done in Europe using the Sierra air booster as a doner block.
Masterline were at the time working on a 2 stage version we discussed this with them at DEMA and Rix I recall
But pretty much eveything from the original Sierra got canned and re designed and it was a long time ago.

The rings were changed to Kalrez,
The valves changed to ceramic,
The valve springs changed to monel.
The pipework tubing changed to Alpha brass
The 1st stage piston diameter was increased
The inlet pressure was reduced (client requirement)
The 1st stage head was redesigned to reduce the sharp gas approach angles and in bronze
Interstage RTD's were fitted with hi temp cut outs
Sintered bronze oversize cone element filters were used reducing Dp and clogging
Inlet 20-40 Mu interstage 10-20 Mu outs 2Mu also to reduce clogging and particulate from worn ring material
Low Inlet pressure cut out
High Discharge pressure cut out
Interstage cooling was improved using a thin wall pressure break for safety
Interstage relief valves were fitted (ported vents)
RPM adjusted for 50Hz operation and flow requrement
NRV's were added
Cooling Fan was improved 8 blade zero degree pitch angle
Running hours rated at 400 hours before seal ring change at 207 bar

 

[rddvet]

I can take a photo when I get back from diving in a few days. When I had a sierra the cost to have masterline convert it was enough that I just bought a new one. At least you realize masterlines are two stage not single stage. When I was searching the internet trying to learn how to convert it myself everyone kept claiming that a masterline is just a sierra thats oxygen clean and when I would try to explain to them that its two stage theyd say I was nuts. My conpressor guy actually wanted to have a go at doing the conversion as well but I dodnt go that route. I was afraid if he didnt actually know what he was doing I’d be burning my house down.
Its really hard to get info on all of the differences between the two. Ian shared the most info I’ve ever seen someone post about them.
The guys at masterline are pretty good at answering questions. They dont seem to hide their trade secrets if you ask.

 

[Wookie]

+1 on information I had no idea about, thanks Ian.

 

[tbone1004]

@iain/hsm I saw you had a few pictures posted but they didn't show much. I assume the seals and rings and what not are all custom and not off the shelf parts? Good call on the RTD's I have them on my Rix SA6, and not a bad idea to stick them on this as well. Do you remember the temp limits you set?

@rddvet I'll call them Monday and see if they are actually using a reduced first stage to make something more akin to a Haskel 15/30 or if both stages are still the same size. If they're both the same size then it won't be terribly difficult but I think the biggest thing is reducing the RPM to keep the thing cool

 

[iain/hsm]

@iain/hsm I saw you had a few pictures posted but they didn't show much. I assume the seals and rings and what not are all custom and not off the shelf parts? Good call on the RTD's I have them on my Rix SA6, and not a bad idea to stick them on this as well. Do you remember the temp limits you set?

Heck I cant remember what I had for breakfast let alone all those years ago. But the general rule of thumb with RTD's on our oxygen compressors is two fold.
1. Make sure the thermocouple is as close as you can get it to the hottest gas point i.e. just off the discharge valve without blocking the flow path. And don't use those stick on tab types and have them cooling off in the fan breeze or mount it half a mile away down the pipe from the red hot head discharge side.

2. And second for oxygen compressors set them around 10C to 15C above the nominal maximum operating temperature you measure during the hottest part of the day or fill process/temperature. Ie At the hottest point or you will be jacking about with it all day long. This will vary depending on your inlet pressure, discharge pressure, ambient air cooling temperature and make and model of the compressor itself.

The finer details are to have a digital display that shows both the running temperature and a separate display that shows the cut off set point temperature, Gives you the opportunity to adjust it while running if your getting close. They are normally a green display and a red display I like them.

Also remember we are British over here and work in proper mathematic calculations in this case centigrade and the kick off temperature setting for European builds is 175C. That way we meet the Electrical safety rules over here EEx 3 and T3 for the temperature requirement set at 175C with a maximum allowed of 200C in the standard. Its a bit like your Yankee NEMA4 or NEMA 7

175C (350F) is also the maximum temperature you want to get Viton seals and O-rings at. So you start there as a setting to kick off then dial it down when commissioning to 10-15C above your maximum temp produced.

If it kicks off too often then simply dial it up by 10 degrees C from your lowest measured set point.

And another point while we are at it on o-ring material, IMHO only use Viton O-rings with both a known cure date and batch number or compound number. Do not use or be fobbed off with FKM when compressing oxygen. Thats enough for now I guess. Iain

 

[iain/hsm]

Heck This will take ages to explain. I should also add we are taking about the actual gas temperature.
And not the head temperature measured say by an infrared heat gun or tab back RDT surface mounted.
Nor the cooling coil tube temperature. All these measurements are much lower that the real gas temperature (before cooling) Hence why you mound the RTD sensor in its own thermowell right up into the valve or as close as you can get.

Further by measuring the hottest component (the gas) and not the surrounding metal parts you get a more accurate measurement but also a quicker reaction time should something kick off
No point fitting a RTD half a metre past the final stage cooling coil on the cold side when it's the 1st stage on fire. Iain