Author Topic: VAC SYS vacuum decay times  (Read 9890 times)

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Offline Cheese

  • Posts: 9756
VAC SYS vacuum decay times
« on: May 14, 2016, 01:26 PM »
This post is rather lengthy, so if you don't want to read all the details or are a firm advocate of the "One Minute Manager" philosophy, just go down to the conclusion. Let the snoring begin...

This post is in response to a thought I posted about 3 weeks ago. At that time I turned over my newly purchased VAC SYS base and noted the vast vacuum chamber contained underneath. My first thought was that this could potentially be a buffer mechanism if utilized, for a catastrophic vacuum failure. I decided to see if this was indeed the case.

I used a 12” x 12” x ¼” piece of ply to adhere to the vacuum head. The ply was sanded with 180 grit Granat to approximate what the typical usage may entail. The piece of ply is of very light weight and was chosen so that when the vacuum pump was turned off, and when the vacuum had reached a critical level, the spring loaded, green poppet valve, would lift the ply free from the vacuum head and I could then easily record the length of time the ply had been secured to the vacuum head.

So I ran a series of 3 timed tests, and averaged them, not to come to a definitive decay value, but rather to ensure that the short time testing values were indeed indicative of something substantive.

Initial testing was with a Festool clamping module SE 1, connected to a Milwaukee vacuum pump using Festo/Festool vacuum hose, fittings & clamps.

The vacuum was pulled down to 500 mm Hg and allowed to stabilize. The vacuum pump was turned off and the 12” plywood square popped off of the vacuum pad in 9, 10.5 & 11 seconds = 10.2 seconds average.

I then engaged the green slide switch on the SE 1, which evacuates the chamber underneath the vacuum head and pulls the entire SE 1 unit down into contact with a non-porous surface.

The vacuum was again pulled down to 500 mm Hg and allowed to stabilize. The vacuum pump was turned off and the 12” plywood square popped off of the vacuum pad in 113, 112 & 108 seconds = 111 seconds average.

Conclusion:
There is a substantial vacuum reserve available if the vacuum in the SE 1 base is utilized rather than just bolting the SE 1 to a table/bench. It increases the hold time by a factor of 10
   [cool]   [jawdrop]

Note:
The amount of vacuum that can be generated is dependent upon the surface finish of the component being placed on the vacuum pad. In this situation, the sanded plywood would only allow the pump to pull 500 mm Hg, while using phenolic coated plywood/plastic, the pump can pull over 700 mm Hg.

Along with surface finish, the more vacuum that is pulled, also increases the decay time significantly. I’ve worked with phenolic coated plywood, switched off the pump and 45 minutes later, I could not remove the plywood from the vacuum head because there was still over 450 mm of vacuum in the system. 

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Offline neilc

  • Posts: 3077
Re: VAC SYS vacuum decay times
« Reply #1 on: May 14, 2016, 05:27 PM »
That's a good test. 

I normally have the Vac Sys sucked to a piece of masonite on my MFT table or to the top of my bench. 

I recently made the vertical Vac Sys holder that clamps to the front of the MFT via the side rails as shown by @erock in his video and noticed the reduced decay when I did not have the reservoir enabled.  Your tests confirm why!

Offline Jesse Cloud

  • Posts: 1752
  • Festooling at the end of a dirt road in New Mexico
Re: VAC SYS vacuum decay times
« Reply #2 on: May 14, 2016, 06:13 PM »
Thanks Cheese.  Great post.

Offline Kev

  • Posts: 7654
Re: VAC SYS vacuum decay times
« Reply #3 on: May 14, 2016, 10:59 PM »
Thanks for doing this - very useful insight.

Offline Cheese

  • Posts: 9756
Re: VAC SYS vacuum decay times
« Reply #4 on: May 15, 2016, 12:22 AM »
The other dimension to this situation that piqued my thought process, is there have been several FOG members that have been actively wanting to adapt a venturi type vacuum pump to actuate their VAC SYS. To the best of my knowledge, these systems are an open looped system. This means that if the compressor quits supplying air to the venturi for whatever reason, there is no reservoir/buffer backup system for the vacuum which means that the system decay time is only a matter of seconds as it is now open to atmospheric conditions. Just food for thought.

Bottom line is, that overall Festool does do their homework, and if we want to modify their equipment for our own specific purposes, we need to do our own due diligence to prevent bad things from happening.
« Last Edit: May 15, 2016, 10:07 AM by Cheese »

Offline Lbob131

  • Posts: 568
Re: VAC SYS vacuum decay times
« Reply #5 on: May 15, 2016, 07:47 AM »
What is a  "decay  time"?

Offline Kev

  • Posts: 7654
Re: VAC SYS vacuum decay times
« Reply #6 on: May 15, 2016, 10:27 AM »
What is a  "decay  time"?

@Lbob131 there are a lot of explanations that vary relating to context and can be very complex.

Interpret here that the "decay time" is a time period from which the vacuum level within the "system" degrades (leaks in air and gains pressure) to a point where the vacuum clamp can no longer support the clamped item.

Offline leakyroof

  • Posts: 2384
Re: VAC SYS vacuum decay times
« Reply #7 on: June 14, 2016, 11:08 AM »
What is a  "decay  time"?

@Lbob131 there are a lot of explanations that vary relating to context and can be very complex.

Interpret here that the "decay time" is a time period from which the vacuum level within the "system" degrades (leaks in air and gains pressure) to a point where the vacuum clamp can no longer support the clamped item.
  Of course in his own shop, Kev would refer to this as the Oh Sh#$@$% time that he has to run and grab the Vac-Sys before tragedy strikes..... [poke]
Not as many Sanders as PA Floor guy.....

Offline Kev

  • Posts: 7654
Re: VAC SYS vacuum decay times
« Reply #8 on: June 14, 2016, 10:08 PM »
  Of course in his own shop, Kev would refer to this as the Oh Sh#$@$% time that he has to run and grab the Vac-Sys before tragedy strikes..... [poke]
[/quote]

 [thumbs up] absolutely spot on !!