[PSUBS-MAILIST] air compensation

[Alan via Personal_Submersibles]

Hank,
Hugh is the expert on this, but....
if the supply pressure is 130psi to the inlet port of the regulator, then if there
was a drop of pressure down stream caused by the piston extending, you
would get pressure at 130psi flowing in until the back pressure in the system 
( hose & actuator) reached your set pressure (4psi). It doesn't look
like a simple equation because the 130psi would be flowing in very slowly
initially, as the valve slowly opened. 
   Now to the ascent! If you are using a relieving regulator set at 4psi then the
pressure that it relieves at will be set by the strength of the spring in the handle
controlling the relieving valve.
You could change what it is preset at by buying a new spring or maybe grinding
a bit off it. Say it is set at 2psi above your main setting, then the internal pressure
of the regulator would be 6psi above ambient before it started relieving.
The worst case scenario would be ascending from 30ft where the pressure would
double if it wasn't relieved. Any pressure in the hose is going to increase as will
the flow, so not an easy equation. 
You might want to guess what internal pressure the actuator can take & be careful
of the wire gland fitting that nothing can blow out.
Cheers Alan 

Sent from my iPad

> On 10/12/2017, at 1:53 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Alan, thanks'
> I just googled an air flow chart, and the .125 air hose can supply .5 scfm at 5 psi.  So now I have to calculate the volume change in the actuator  at my dive rate and see if .5 scfm will supply each actuator.  I was not worried about the line supplying the actuator when it was operating.  My concern was for the line to keep up while descending.  I also thought I might need a relief valve on each actuator for rapid ascents.  
> Hank
> 
> On Saturday, December 9, 2017, 5:25:45 AM MST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Alan,
> I assumed that the air pressure at the out port of the regulator is 4 psi above ambient.  My concern is,, will the .125 air line supply air fast enough at 4psi to maintain 4psi above ambient inside the actuator.   
> Hank
> 
> On Friday, December 8, 2017, 10:01:31 PM MST, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Hank,
> you will have the internal space of your actuator to equalise, which
> shouldn't be a problem as this will be slowly equalised as you descend.
> Then you have the piston going out during manipulator use, & there will be air going
> in to fill that void. If you are running either off a 1st stage regulator or a relieving
> regulator like Cliff's, the air will be kept at ambient & it will only be that small
> flow in to the space the piston has vacated. 
> You could estimate the internal volume change by using an on line cylinder volume calculator & plugging in the piston diameter & the difference in length it changes 
> as it protrudes.
> If the actuators full stroke takes (as an example) 4 seconds at full speed, &
> the volume is 100ml, you could then run air through your intended hose at your supply pressure (130 psi for scuba regulator) in to a small crushed plastic bag, & see if it can
> at least fill the bag with 100ml of air in 4 seconds. 
> Have done similar for rough estimates.
> Or just blow through the hose in to a plastic bag ( like lots of people do at Christmas
> time) & you might think yep this will do with 130psi behind it.
> BTW on A relieving regulator the orifice is pretty small & in Cliff's case it is venting
> the internal volume of his 4 thrusters in the last 30ft of ascent.
> Cheers Alan
> 
> Sent from my iPad
> 
>> On 9/12/2017, at 4:37 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> Hi All,
>> I am new to air compensating so I need to know if the air line size to each of my actuators is critical.  To save money I want to recycle  the high pressure nylon tubing that is used for hydraulic lines on my hydraulic arm.  The nylon air lines  are a bit over .125 ID
>> thanks'
>> Hank 
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