[PSUBS-MAILIST] Pressure Test Chamber

Wed Jun 21 23:19:51 EDT 2017

Hi Steve,

Scuba compressors do “explode” ( combust oil) .  i.e. the oil turns into carbon on high temperature.  Synthetic oils have a much higher flash point.  A relief valve is not necessarily going to protect from an explosion.

The essence is that it comes down to the temperature of the achieved compression.  Scuba compressors normally have a compression ratio of between 3.5 – 4.5 in each stage. In API 618 or 11P ( Compressor Standards) it states a maximum temperature of 300 deg F (618) – 350 deg F (11P)  and generally industrial compressors will not go over a compression ratio of 4:1.  If the pressure starts off at 0 psi and ends as say 2000 psi then the compression ratio is approx. 135:1   and as the final adiabatic theoretical temperature is =T1 x  R^((k-1)/k) = 520 x  135^(.4/1.4) = approx. 1600 deg F assuming no temperature loss etc.  So I don’t consider it is OK to sanction an air over oil compression as the average punter does not understand the significance of fast compression and slow compression.  What happened in our case is that my son had tested a number of valves and then after smoko opened the valve too quickly creating a high temp shock wave which obviously ignited the oil in the pipe.  We have also seen pipes blown off hydraulic compressors hospitalising an operator which had air ingress.  

We make high pressure gas compressors up to 600 hp. And serviced many other makes and models.  We also make high pressure valves up to 10,000 psi.   If we test on air we have sometimes had the seats spontaneously ignite.  There is a reason for testing on Nitrogen or inert gas or using water.  

P-subs used to have guys playing around with 150 psi but now there are some serious pressures being bandied about by guys without Engineering degrees.  Hence my cautionary tales to Alan and publishing on P-subs. 

Cheers,

Hugh

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Stephen Fordyce via Personal_Submersibles
Sent: Wednesday, 21 June 2017 7:40 PM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Pressure Test Chamber

Hi Hugh & Alan,

Good point to consider, but it would depend on the flashpoint of the oil.  SCUBA compressors do the exact combination of pressure/air/oil and don't explode.  Diesel engines do too - sort of, anyway.  Mineral oil designed for compressors would be a good option although pricey (AU$200 for 20L recently). Shell Corena P150 mineral oil is what I use.

High pressure air is a mechanical hazard to be considered in and of itself.  I'd highly recommend installing a relief valve (or device) on any test chamber or other vessel.

Cheers,

Steve

On Wed, Jun 21, 2017 at 2:28 PM, Hugh Fulton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Alan,

Never pressurise oil with air to those pressures.  An explosion waiting to happen.  Oxygen partial pressures!!

If you want to do it use nitrogen.

Hugh

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of james cottrell via Personal_Submersibles
Sent: Wednesday, 21 June 2017 3:34 PM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Pressure Test Chamber

Alan,

Pressure testing that high needs to be done with liquid not gas. High pressure air is VERY dangerous. A pressure washer pump using water would be a safer choice.

Greg

  _____  

From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
To: personal_submersibles at psubs.org 
Sent: Tuesday, June 20, 2017 9:01 PM
Subject: [PSUBS-MAILIST] Pressure Test Chamber

I am making a plastic container to fill with water & stand inside my

pressure chamber. There is a gap between the wall of the container

& the chamber which I intend to fill with oil. There will be about an

inch of air at the top of the chamber & I'm using a scuba tank to

pressurise the unit up to 3000psi.

Will car engine oil do to fill the gap between my plastic container &

the chamber wall, or do I need to go with a hydraulic fluid.

Am using the plastic container to keep water from rusting my test

chamber. (Aussie Steve's idea)

Cheers Alan

Sent from my iPad

_______________________________________________

Personal_Submersibles mailing list

Personal_Submersibles at psubs.org

http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

 <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> 

Virus-free.  <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link> www.avast.com 

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20170622/1dde3030/attachment.html>