Maximator Booster Pump

Skipbreather

Hi Steve-

When it comes to O2 fires, you need to reorient your thinking. The tanks, whips, and booster THEMSELVES become the fuel! You are absolutely correct to isolate the O2 supply, but when that’s done the ONLY option is to run like hell!

Please understand I’m not throwing rocks here- just trying to keep you alive.

I see grave potential for some problems when combining your hardware and procedures. Specifically, heat is you enemy and your hardware- originally intended for use w/ liquids- is not designed to dissipate it well at all when used w/ gasses. If one adds to the heat build up by cycling the pump rapidly IMHO it is only a matter of time until you have a very, very bad day. I would submit that a precise method, such as a needle valve, to control your drive gas is absolutely essential for safety.

I use a nitrogen booster that I converted. It has been totally disassembled & O2 cleaned. I binned the aluminum head and machined a new one from bronze. The check valves are O2 compatible Swagelok stainless. I have found that in operation the highest temperatures- by FAR- occur at the high side check valve. When it begins to feel even modestly warm, I throttle the drive gas flow rate- not the pressure- to slow the cycling down.

The layout of your booster shows the high side check valve buried inside the head/ cylinder combination, where all of the various sources of heat get to join forces and look for something to ignite. That does not mean you cannot use it safely to boost O2, but to compensate for the design shortcomings you need to develop procedures that address them, paying close attention to the real time temperature of your system.

There’s an old saying about how those who do not study history are doomed to repeat it. Long before this board came to be there existed- and still exists- the Rebreather Mailing List. This thread keyed my memory and I went looking in the archives. Two posts by Joe Dituri and Rich Pyle that should be required reading for ANYONE boosting O2:

http://www.nwdesigns.com/rbarchive/2000/3797.html.gz

http://www.nwdesigns.com/rbarchive/2000/3802.html.gz

Do not be afraid of high pressure O2, but respect the hell out of it!

Very best wishes,
Ken

iain-hsm

Matt.
The piston head material argument is frankly wrong. Diesel engines have no spark plugs to ignite fuel. In an engine the cylinder pressure is only 16 barg (234psig) and at only 16:1 ratio yet the temperature becomes high enough to ignite the fuel without a spark plug.

iain-hsm

The math’s involved is compressing oxygen from low pressure to 250 barg needs three things to be considered first.
1. COMPRESSION RATIO. To avoid over heating oxygen (adiabatic compression) the maximum compression ratio of inlet pressure to outlet pressure should never exceed the maximum 5:1. Therefore if the minimum inlet pressure was say 20 barg and the maximum outlet pressure required was 250 barg it therefore should be clear oxygen should be compressed in a number of stages of compression and not in a single hit.

2. HEAT GENERATED. Each stage of compression creates a specific heat load therefore the maximum gas temperature for oxygen during compression should be specified by the equipment supplier and by bomb testing each of the components. For the sake of safety the designer should also reduce this temperature as the pressure increases. Please note that gas temperature is not the same as the pump temperature. Gas flow and the pump casings act as a heat sink but the metal temperature is not used in oxygen design calculations.
3. FLOW VELOCITY. Gas flow volume, the gas speed and gas viscosity due to compression will create friction to the internal component parts passages as will the specific heat number of the gas being compressed. Again for brevity assume Air Oxygen and Nitrogen in the middle of this range and the same, with Helium and Argon being at opposite ends of the scale in heat generated.

If you take a maximum cut off temperature of 95C (205F) when at 250 barg (3625 psig) and a say 140C (280F) at lower pressures. For oxygen it calculates out in three stages as follows:

Stage One. Inlet 11 barg (160psig) compress to 39barg (560psig) will produce 120C (250F) gas temp with a compression ratio of just over 3:1.

Stage 2. With the 39 barg cool back to 30C and compress to 120 barg (1740 psig) Again about 3:1 and again with a gas temperature of 120C (250F)

Stage 3. Once cooled back to 30C compress from 120 barg (1740 psig) to the final pressure 250 barg (3625 psig) At a ratio of 2:1 Producing a gas temperature of 80C (175F) at the point of compression.

Note: Gas temps are at the point of compression (ignition point) not on the casing hoses or cylinder. Iain Middlebrook

iain-hsm

JT
Running a booster pump to compress air from the atmosphere is frankly daft. Take a guess where all the condensed water from the atmosphere is now!!! It's in your booster, in your hoses, in you cylinder and whetever it is you filled, happily rusting away!!! Suggest you use an air compressor for ambiant air that way you get a water separator and filter with it to drain the pump of water you have collected!! Your not getting good advise on this product suggest a refund under the sale of goods act!!

Genesis

Nod-nod to all of the above.

As far as being able to put out an oxygen-fed fire, forget it. If you can't shut off the O2 flow then you're not going to put it out so long as the supply lasts.

You thus have to concern yourself with "what can burn?" The answer in pure O2 is "nearly anything." Just about the only "safe" material in that situation is brass, which will not burn up to roughly 10,000 psia of pure O2. Stainless, teflon, ordinary steel, iron - all burn mightily. Aluminum burns in pure O2 at relatively low pressures almost like magnesium does in air!

If the answer "run like hell" is not acceptable if you have an "event", then you have to look at "hardening" your installation. Some of the ways you can do that include:

1. Placing the supply cylinder(s) on the other side of a stout and firerpoof (e.g. reinforced CBC) wall, with brass tubing going to the cylinders. The idea here is to be able to get to the valves on the tank(s) to shut off the O2 flow without having the fire burn its way up your supply tubing! You can also put a "deadmans" switch and solenoid valve at the tank, but you need one rated for high pressure O2 use - that's likely to be hard to find and/or expensive.

2. Placing flow restrictors inline (again, made of brass) with the supply at or very near the supply tank(s) for the purpose of preventing runaway flow in the event of a fire. Flooding O2 from what amounts to an effectively open cylinder valve will cause the fire to go from "burning" to "conflageration" almost instantly. Restricting the flow slows the propagation of any fire that gets initiated. These have to be sized such that the necessary feed rate is met - but no higher.

3. Paying very careful attention to cycling rate and heating. This has been covered well already.

If you want to see how bad this can get and how fast, take a welding torch (your O2 source), find a fire-safe place, and ignite something quite ordinary with a lighter. Then, wearing proper protective clothing and standing safely away, direct a jet of O2 from the torch head (no acytelene) onto it. Note what happens.

Multiply that "increase" in combustion speed by about a thousand if you have an unrestricted O2 flow available from an open O2 supply tank......

iain-hsm

INSTUCTIONS FOR FILLING WITH OXYGEN.

Before running away.
1. FIRST..........Remove the cylinders from rig. lol

Attached Images

fire_2002.jpg (151.5 KB, 259 views)

Genesis

That would suck really badly if it happened underwater

Northern Monkey

I did not what to get drawn into this discussion but contamination is a greater risk than the above.

Somebody mentioned a diesel engine, sorry a 60 rpm fuel less pump is a little different to an internal combustion engine that idles at 1000 rpm with fuel injected.

Secondly, these small pumps barely rise above the ambient temperature, as many of the users can verify.

I am in discussion and know that Maximator are working on a mini rebreather oxygen booster. Maximator now realise there is a market for a small pump (ie 20 times smaller than the commercial units) that is affordable for increasing number of rebreather divers. The large commercial pumps will pump oxygen quicker but provided that the ratios are the same both large and small pumps will use the same volume of drive gas to pump the same volume of boosted gas, it just takes longer, not a problem to a rebreather diver.

The major concern with booster pump design is cross contamination of drive gas and booster gas. Commercial boosters are designed such that the booster chamber is physically separate from the drive side. This is to prevent commonly used "industrial compressed air", which carries oil and water, having any chance of coming into contact with the oxygen. The mini booster must be driven with breathing quality air, although cleaning, lubrication and other modifications have been made to these pumps.

I agree that commercial boosters that are working 24/7 and shifting large volumes of oxygen need cooling and it becomes an issue even to the extent of using water cooled jackets over the boosted gas cylinder.



Booster Ratios????, there are two ratios banded about.

Pump efficiency ratio, this is the ratio of drive pressure to the outlet pressure. 1:30 or 30:1 means with a drive pressure of 10 bar can produce an outlet pressure of 300 bar. Practically its more likely to be 280 bar.

The other ratio is the boosted gas inlet and outlet ratio, many manufacturers including Haskel specify that the pump is only efficient at a ratio of 1:5 for oxygen and 1:3 with helium. This is saying: make sure your inlet gas pressure is within this ratios for the required outlet gas pressure otherwise you will be waiting a long time and use infinite amounts of drive gas. (Jetsam website has specific details on the volumes). So for 250 bar out you need over 50 bar in the supply tank. for O2 You overcome this by cascading from 50 litres to say 10 litres then to 2 or 3 litre CCR cylinders.

I hope this sheds more light on the subject, and I will keep you posted on Maximators new pump in 6 months, in the meantime I have pumps available to use at your own risk.

Mark

underpresurediving.co.uk

__________________
Death is not an option!

iain-hsm

Therfore the product should be supplied with a inlet micronic filter

Quote: (Originally Posted by Northern Monkey)

Somebody mentioned a diesel engine, sorry a 60 rpm fuel less pump is a little different to an internal combustion engine that idles at 1000 rpm with fuel injected.

The example is just how little compression is required to create ignition both in terms of presure and ratio.



You forget that the gas temperature is the relationship between compression ratio, specific heat and compression ratio. This has nothing to do with what you can feel. Its like having a SCUBA cylinder with a 3 inch wall thickness filling fast and saying it doesnt get even warm LOL Iain Middlebrook

iain-hsm

Mark.
What would shed a better light is the smallest hint of a certified "fit for purpose" for the product and that my friend requires a CE mark.

Just show that the pump is suitable for Oxygen at X inlet pressure and at an X outlet pressure and that it has a CE Cert and its not a problem, your case is sorted.

The problem is divers will buy this product and not have a clue as to its suitability or the risks they and others around are taking when using it.

I am interested how you can sell a product to the public "AT YOUR OWN RISK" for filling oxygen cylinders. The supplier is required by law to have both product liability and certification. Would you like to sell me one of these pumps for filling oxygen cylinders and I can show you what this can mean to the supplier?
Let us know what test certificates comes with this unit. Please answer what independant certification you have for this product.

Frankly contamination may be the least of my worries with selling a pump "At my own risk? You have got to kidding" Iain Middlebrook.