Date: Wed, 12 May 2021 11:46:03 -0700
Reply-To: Alistair Bell <albell@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@SHAW.CA>
Subject: Re: Cold start oil pressure
In-Reply-To: <20714851-527B-47E4-96ED-99109DB5BBD2@comcast.net>
Content-Type: text/plain; charset=utf-8
Yeah, i understand the compressibility of gases etc.
And yes, air in hydraulic systems will result in lost motion. I’m your example the air will get compressed rather than the bucket moving the dirt :-), as the gas bubble compresses. But it will move in the end if you haven’t run out of travel in the piston.
The air bubble is acting like a spring. But don’t forget that in a closed vessel the internal pressure is equal thru out.
Back to the spring analogy, the bubble will dampen transient changes in pressure, but will not change the overall pressure. Just as you car springs work on the van. The springs support the weight of the van. A load cell at the bottom of the spring will read the same as one on the top of the spring.
So that’s why I think an air bubble in a tube leading to a pressure gauge ain’t a big deal. It will dampen transient pressure spikes but overall pressure will be unaffected.
You tire pressure gauge doesn’t care about air. I don’t recall bleeding gasoline from my fuel pressure gauge when I tested that in the van.
And we just got our waterjet table up and running at work. The big pressure gauge is teed off the main line to the cutting head. A tee then a vertical to the gauge. It wasn’t bled. Reading 55,000 psi right now as I write.
Alistair
> On May 12, 2021, at 8:37 AM, OlRivrRat <OlRivrRat@comcast.net> wrote:
>
> Air is said to be 10,000 times more compressible than oil ~ In any Hydraulic Line, if there is an
>
> Air Bubble Between the Oil & the Device It needs to move, the Air will get Compressed Rather Than the
>
> Device Getting Moved ~ It’s what makes Hydraulics so much more Efficient that Pneumatics ~
>
> Easily understandable example > What effect does an Air Bubble in Your Vans Brake Lines have on
>
> Your ability to Apply Necessary Force to the Brake Cylinders ~
>
> Of course it there is an Air Bubble trapped between the Oil in an Extension Tube & a Pressure Sensor
>
> @ the end of that Tube it can easily be gotten rid of by simply Carefully Loosening the Sensor while the Eng’
>
> is Running thereby allowing the Air to be forced out & replaced by the Oil ~
>
> ORR ~ DeanB
>
>> On 12 May , 2021, at 1:10 AM, Alistair Bell <albell@SHAW.CA> wrote:
>>
>> I’m slow.. I don’t see how an air bubble will affect it much. Oil presses bubble, bubble presses sender.
>>
>> Just like a tire gauge :-)
>>
>> Alistair
>>
>>
>>
>>>> On May 11, 2021, at 10:38 PM, OlRivrRat <OlRivrRat@comcast.net> wrote:
>>>
>>> They will work just fine as long as You Can Avoid getting an Air Bubble between the
>>>
>>> Sender & the Fluid ~
>>>
>>>> On 11 May , 2021, at 11:11 PM, Alistair Bell <albell@shaw.ca> wrote:
>>>>
>>>> I’d like that explained to me. I mean the problem of having an oil pressure sender on a tube.
>>>>
>>>> I’m not being coy, I mean it. Purely mechanical oil pressure gauges are at the end of a tube, why not an electrical sender?
>>>>
>>>> Alistair
>>>>
>>>>>> On May 11, 2021, at 9:42 PM, OlRivrRat <OlRivrRat@comcast.net> wrote:
>>>>>
>>>>> IMHO, placing a Sender/Sensor, be it Pressure or Temp, @ the end of a Dead End Tube
>>>>>
>>>>> is a Very Bad Idea > In the case of a Temp Sensor it could be next to impossible to get Fluid
>>>>>
>>>>> to it that is Relevant & in the case of Pressure,, If You happen to end up with an Air Bubble
>>>>>
>>>>> Trapped Between the Fluid & the Sensor You Most Probably May Not get Accurate Readings ~
>>>>>
>>>>> ORR ~ DeanB
>>>>>
>>>>>> On 10 May , 2021, at 9:43 PM, Gene P <olgreywoof@GMAIL.COM> wrote:
>>>>>>
>>>>>> Hey folks,
>>>>>> 87 Wolfsburg 2.1, original everything
>>>>>> I don’t think this is a problem, I’m just wanting to learn something.
>>>>>> For years I’ve had VDO oil pressure and temp gauges, senders on a sandwich adaptor at the oil filter. Start-up pressure has been just under 80, right at the top of the gauge, in any season.
>>>>>>
>>>>>> As part of a recent project, I pulled the sender between the pushrod tubes and put that with the VDO sender on a tee about 7 inches forward of that port. Now start-up pressure is about 55-57. Would moving the sender in that manner cause a change, or that much change, in the reading?
>>>>>>
>>>>>> The other change I made (burying the lead I think) is switching from Castrol 20W/50 to Mobil1 15/50 for the first time. Does synthetic oil make that much difference in start-up pressure?
>>>>
>>>
>
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