Thread Tools
Apr 15, 2019, 10:17 AM
Registered User
Thread OP
Quote:
Originally Posted by kablair
Tom - I admit to not being a vaccuum pump expert, but I've always understood a unit being rated for continuous-duty would not be subject the type failure you're describing. The particular unit I have was hospital surplus and they ran them continuously for years at a time. Perhaps I'm not understanding that correctly???

You're right about the 'full max vacuum'. There was a project that needed less vacuum so I installed a tee between the bag and the pump, with a cheap ball valve, and opened the valve to create a 'leak' that reduced the amount of vacuum.

Could you share more info on that continuous-duty pump failure? I'd like to learn from your experience.
Thanks,
-Keith
Hi Keith: No expert here either, just an old builder. The one vacuum pump that stopped working, I opened up and found the thin metal reed valve to no longer be flat, so it would not seal the opening that it was covering. It was about 1/2" wide, square on end with one corner clipped so it would fit only one way. It was bout 3/4" long and a 180 curve on the other end. It was the thickness and shape of 0.020 feeler gauge. There was a clamping metal tab and screw that held the reed valve in place on the square end. When putting the head back on, I noticed there was a recess that needed to be aligned over the reed valve for clearance. It worked for vacuum, but when the vacuum switch was calling for vacuum. the motor would struggle to come back on because the piston stroke could not overcome the vacuum in the suction line at 17 inches of Hg. When the vacuum dropped down to 10 inches of Hg, the pump motor would start, and the vacuum would go back up to 20 inches of Hg. This is when I concluded that the pump was not able to over come the vacuum in the line between the on way check valve and the pump. To test my conclusion, I ran the system , waited for the vacuum to be pulled to 20 inches and when the motor shut off, I removed the vacuum hose from the pump inlet. Put the hose back on and waited for the vacuum switch to call for more vacuum; when that happened, the pump motor started instantly. My temporary fix was to poke pin holes in the vacuum hose to cause the line to go to atmospheric pressure when the motor was off. The pin holes did not open up adequately until I put a weight of the line to keep it curved in the section of hose that had the pin holes. When the pump came on, the vacuum would straighten out the hose enough to close off the pin holes enough so a vacuum could be pulled. So his is why I am going to use the solenoid solution to relieve the vacuum in the suction line between the check valve and the pump.

Tom f.
Sign up now
to remove ads between posts
Apr 15, 2019, 10:28 AM
The Junk Man
Quote:
Originally Posted by kablair
Two words - “continuous duty”

I dread the day my little Gast MAA-V103-MB dies. It runs continuously, easily pulls 25” of hg, and is very simple.
-Keith
It will never die. Rebuild kits for that, and other GAST pumps, are readily available. And easily installed.

I have a GAST PA-704 that will outlive me. And the next owner.

Tom
Apr 15, 2019, 10:40 AM
Registered User
Thread OP
Hay guys, I understand that there many ways to do stuff. Lots of solutions depending on what you are trying to do. To maintain a vacuum lower that the maximum available and to not have a continuous running pump was my goal. Another solution might be a two stage vacuum pump. I think that I have found what will work for me.

Tom f.
Apr 15, 2019, 11:03 AM
Registered User
There is rarely one "right" way to do things. Hence it is always interesting, if not often humbling, to learn on these forums what others are doing.

I'm glad you found the right solution for you,
-Keith
Last edited by kablair; Apr 15, 2019 at 11:04 AM. Reason: left out a word...
Apr 15, 2019, 10:47 PM
Registered User
hobiepilot's Avatar
Quote:
Originally Posted by TomFlyer
Hay HobbiePilot: this is basically the same setup recommended for use with a MAC valve. But why the second small vacuum tank? The vacuum in the line going into the pump will go to atmosphere with or with out the small tank.

I now have my 110v solenoid valve and hope to hook it up today. I will post how it works.

Tom f.
Depending on how fast your pump starts, it might not be needed. The trick is the solenoid that removes the vacuum from the lines to the pump.. and the rest of the system being isolated by a check valve. Plumb it without a chamber, and if the motor spins up, all is good. If you have minimum plumbing, the vacuum in that small volume will drop in pressure fairly quick.. so a small (and cheap) tank, just means it can spin "easy" for a short while. A alternate would be to start the motor, and THEN close the solenoid. Timers cost more than a few pieces of plastic.

As for Continous duty.. my Gast pulls 10.8 amps. Uh gee, that's only 31,104 watt-hours in a day!! So.. like they say, you CAN keep the barn heated WITH the doors open, if you have a big enough heater. I prefer to conserve energy when I can.. and a piece of scotch tape will seal a hole in a vac bag! But.. to each their own.
Apr 15, 2019, 11:03 PM
Registered User
hobiepilot's Avatar
Reading the last few posts.. there are two easy solutions to not needing a full vacuum. And like with foam wings, excessive vac will crush them. So you can buy a genuine vacuum regulator.. just like a pressure line regulator, with adjustment knob and all.. so you have no leaks. No need to run continuous. The other option that I use, is a tiny pump.. which also came out of some medical testing device, that is even smaller than the 12V tire inflators (that look more like a .45 size model engine, with a drill motor to spin them). The little vac does use a diaphragm, where my Gast is a "vane" pump. I suspect some just buy an aquarium pump, and use the inlet side. But the little one just runs on a small electric DC motor, so it's not using hardly any power.. and at the lower draw, it's fine. I bought the regulator too, just haven't done the plumbing yet. Vane pumps have a large disk, with movable vanes, which are thrown outward against a shaped cavity. As the vanes move, they draw the vacuum.. while running smoothly against the cavity wall. No check valves there. And if you are not aware.. you should have a catch bottle, near your bag set-up. If there is any excess of epoxy, it goes into the jar, and none of it gets sucked into the pump. A very not good situation.
Apr 23, 2019, 08:26 AM
Barney Fife, Vigilante
tom43004's Avatar
I have a continuous duty Gast pump with a bleed valve and have been building with it since the 80s. I actually have three of them that I've collected over the years but I only use the original. I've probably bagged / molded over 500 parts with it. It's stupid simple and IMHO indestructable.

I did acquire the parts (mac valve, solenoid, vac switch, etc) to build a full system a few years back but I've never felt the need to assemble it.

I also have never used a catch bottle except when doing infusion. I've been lucky a few times, with some resin uptake into the vacuum lines, but never reaching the pump, which sits up on a shelf. Maybe I should at least invest a few minutes to plumb in the bottle.
Apr 23, 2019, 04:39 PM
Suspended Account
Quote:
Originally Posted by tom43004
I have a continuous duty Gast pump with a bleed valve and have been building with it since the 80s. I actually have three of them that I've collected over the years but I only use the original. I've probably bagged / molded over 500 parts with it. It's stupid simple and IMHO indestructable.

I did acquire the parts (mac valve, solenoid, vac switch, etc) to build a full system a few years back but I've never felt the need to assemble it.

I also have never used a catch bottle except when doing infusion. I've been lucky a few times, with some resin uptake into the vacuum lines, but never reaching the pump, which sits up on a shelf. Maybe I should at least invest a few minutes to plumb in the bottle.
I can totally understand that, I have an R&G continuous lab pump myself - very compact and absolutely carefree ("lots" of hours), 2 continuous 12v brushless pumps, 1 2-stage 12v continuous brushless pump and I recently acquired a 2-stage hi-voltage continuous membrane pump (Chinese, very affordable and a solid piece of work too).

So you actually don't know what it is to work with a system that you built yourself and that tick tack like clockwork? If you're a regular user like I'd guess you are - you don't even need to turn it off... ever.
May 13, 2019, 05:31 AM
Registered User
BywongFlier's Avatar
Quote:
Originally Posted by hobiepilot
Reading the last few posts.. there are two easy solutions to not needing a full vacuum. And like with foam wings, excessive vac will crush them. So you can buy a genuine vacuum regulator.. just like a pressure line regulator, with adjustment knob and all.. so you have no leaks. No need to run continuous. The other option that I use, is a tiny pump.. which also came out of some medical testing device, that is even smaller than the 12V tire inflators (that look more like a .45 size model engine, with a drill motor to spin them).
I have a cheap no name vac pump and was running continuous with a simple valve leak adjusted for desired vac level. Apart from the vapor leaking oil out the breather I never like leaving these thing on full duty.
Eventually I found a pressure switch from Element14(Farnell) PSF109S-81-330. This switches the pump on and off around a max vacuum that I adjust on the switch. It has a reasonable "dead zone" AKA hysteresis, that is appropriate and is easy to connect if you are handy at SAFE electrical construction. I just have a small gas bottle as a tank and not even a check valve (....yet). This works a treat on overnight cures, with a short burst of motor run every few minutes. Not enough to cause much vapor loss and the pump is cool as our approaching winter. At least I can adjust the max vacuum now to suit foam, ply and lightweight parts.
May 18, 2019, 10:22 PM
Scott
Pylonracr's Avatar
I run a vacuum pump with a 2 cubic foot vacuum storage tank made from 'ABS sewer pipe. I am lucky that my pump will start at near max vacuum with a vacuum switch and relay. You need a MAC valve. simple. Put it in and go forward................

Scott
Jun 10, 2019, 03:10 AM
Entropy is happening!
Jim.Thompson's Avatar

Continuous duty?


Quote:
=BywongFlier;41848251............................. .....
Eventually I found a pressure switch from Element14(Farnell) PSF109S-81-330. ...............................
I used a discarded automotive vac advance diaphragm that a buddy mechanic gave me and a micro switch and capacitor for my regulator. The dead band is adjustable.

Quote:
Originally Posted by kablair
Two words - “continuous duty”
................................... I paid about $100 for mine, and I see several similar ones are available in that range on eBay.
-Keith
The fridge pump for my regulated system was free. And there is an almost endless supply of replacements for the same cost.
In fact, my entire regulated system cost me the price of the vacuum gauge and a capacitor. It's been in commission for nearly 10 years.
Details on my blog for anyone interested in a DIY system. No problem with it starting up under vacuum.

Quote:
Originally Posted by hobiepilot
...........................
As for Continous duty.. my Gast pulls 10.8 amps. Uh gee, that's only 31,104 watt-hours in a day!! .......................
Wow! My fridge pump pulls 1 amp. That is at 240 volts. About 1/5 of the power yours does. We pay around 30 cents Aus per killowatt/hour here.

Quote:
Originally Posted by Pylonracr
I run a vacuum pump with a 2 cubic foot vacuum storage tank made from 'ABS sewer pipe. .................
Scott
Mines bigger than yours!....................
About 100 litres actually. (about 3.5 - 4 cubic foot?).
It started life as a big water pump pressure tank. It was a give away.
I have plumbed it up with the pump connected to the top and the line(s) going to the vac bag at the bottom. That way, it can function as a resin trap should ever any get carried over. It has not happened yet, but always possible.

I find the notion of continuous duty pumps for vac bagging rather curious. Once the bag is evacuated down to the desired pressure, all the work is done. In a regulated system such as mine, the pump runs at as little as 2% duty cycle. Sometimes even less. If it is higher, there is a leak (which often happens).
Why run the pump for that (nominal) extra 98% of the time?


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Vacuum Relief Valve For Sale Curtis Suter Composites Fabrication 0 Dec 01, 2018 09:39 AM
Discussion vacuum bagging material getmeoutofiraq Sailplane Talk 5 Oct 04, 2015 04:07 PM
Discussion 3 way valve for Vacuum Bagging samc99us Composites Fabrication 6 Jan 27, 2012 09:53 PM
Discussion Pressure Relief Valve pyronaught Blimps 1 Jan 17, 2011 03:54 PM
Multiple line vacuum bagging ryancbr Composites Fabrication 1 Feb 18, 2005 06:14 PM