Vacuum pump questions (newbie)

Hey guys just picked up this gast doa-704. I have a few questions. This pump can double as a compressor…so when bagging do i need to hook up some hose and plug of the compressed air side of things(left) or should i just leave it open? Just dont want to kill the pump but i believe the compressed side of things should be closed off.

Second question the little knobs above the guages are to adjust the pull and pressure on each side correct? Right now when i turn it on it just runs Pulling air and blowing…no matter what position the valves are at. Is this correct?

Sorry for the kook questions!!

That’s where the air will come out don’t block it off when vacuuming.

Correct, the knobs will only have an effect when you get some vacuum or pressure. Try blocking the vacuum intake or out flow and the gauges should move. Probably a good idea to only block one side at a time. They’ll display either the the intake vacuum and out going pressure respectively. Don’t get your finger stuck against the vacuum intake! Usually if being used for pressure there would be a filter of some sort to keep stuff from getting sucked in and ruining the interior of the pump. when vacuuming you want to make sure nothing (like resin) gets sucked in. Just use a long hose and you shouldn’t have a problem.

Thanks for the reply! I already put my finger over the vac port. It sucked my finger to it, but nothing crazy i was able to easily remove my finger. Should it be pulling harder?? Just wanna make sure the pump is good to go. Ive heard these gast can run forever.

That is a nice rig but you will need a reservoir between your suction port off vacuum and your bag that you are sucking down. My pumps shut off automatically if they over heat so read your spec Manuel to see if yours does that. I always run a fan on my pumps to prevent fires in the shop. Your set up may or may not have a vacuum switch that you can set to automatically turn pump on and off. they are necessary and easy to set up on the reservoir. Congrats on a very nice pump score.

Is that black thing above the reservoir a pressure switch?

yes from ACP composites. The switch has three prongs and depending on which two you hook up it is pressure or vacuum gauge. Good to have a spare ready to go just in case. Tapped the threads in to PVC easily. Also have vacuum gauge on my reservoir.
Attached photos of full rig inside and rig in the hot house.

I have the exact pump you do. I’ve run it without problems for years. Never had an overheating problem, even when running for a few hours in th summer. It’s quite simple, no oil needed…plug and play. I don’t know why you’ll need a extra reservoir, I’ve always just plugged it directly to the bag.

cool! so i leave the pressure side open while vacuuming thru the vac side?

Your Gast704 pump is supposed to run continuously, it is a medical pump. There is no need for a reservoir tank, or additional rigging. I have the same pump and have ran it for 24 hrs straight. One side sucks, one side blows, the screw knob it to dial down the vac. You should be able to pull about 25-28 mmhg’s with that set up. Super easy set up, super compact… pretty quite too. This is the only unit I have used making vac bag boards.

FYI on the blowing side you can use it for a small air brush compressor, just get the fitting and hook it up. or you can fill a basketball or soccer ball. or on the suck side you can pull pus out of a gaping wound…amazing tool.

Nice purchase.

@ deez
It is a “diaphragm” pump.
if you block the output, it cannot draw air in to create a vacuum.
The air pumped is not being used to cool the unit.

Thanks guys! You all set me straight! Ill post some pics when i get something built with this rig. Just got in soke nice paulownia inneed to mill down.

Just to be clear, does it have to be a “gapping” wound in order to suck out pus?

A reservoir with vacuum switch protects your pump by minimizing running time of this 4 amp device making for a longer operation life before rebuild. Less electric use and lower electric bill. Noise of a continuous running pump will be kept at a minimum in your shop. Diagnosing leaks in a bag is made easier when the reservoir is still pulling vacuum and pump is off. Secondary protection of pump if infusing resin goes bad. All my pumps are 25-30 years old with thousands of board pulls. They came from a dental office equipment sale. I think you are right about that Gast pump being perfect as it is for the job at hand.
I like the channeled board posted.

tank can be really effective if you have regulate air switch on outlet of tank and other pump with regulation, same as compressor tank but for vacuum so you pull more in tank (for exemple -0,7 bars) than in bag (-0,2 for lam up to -0,5 for clamping skin). tank is there a real vacuum reserve and pump work on is one. that’s how work multi outlet installation. possible to have a real stable vacuum with low hysteresis.

Listen to BB30. He has way more experience than you can imagine. He taught me all I know about vac bagging back in 2005, and his experience goes back many years before that. He is a good guy and shares his knowledge if you are willing to listen.

i completely respect BB30 and his work, the dude has made 110’s of vac boards. But with that said, unless you have used the Gast 704 pump, it’s a completely different lil beast. It small and compact and meant to run continuously. It’s definitely not for production vac work, but if you are making one or two boards a month, it more than ample to work as is. We use these pumps at work in our lab, they run continuously all week long pulling 15-23 mmhg. I’ve been at this place for 3 years and they haven’t broken yet? So for what it’s worth, that how I know they work just fine as is. I’ve made a few vac bag boards too.

Attached is my set up. Pump, hose, bag valve. I use the clear Medline blue top cup as a water separator for pulling water out of eps dings. Water goes in cup and not pump…etc. That

That GAST pump a great pump to start with and stick with. My first pump was an ACP 1/16th HP that was the smallest model . It pulled 1 amp when running and would pull vacuum up to 40 square foot projects easily. The owners of ACP were very helpful answering questions over the phone pre internet on vacuum bagging. Happy to say I never had a catastrophe vacuum bagging. always checked every thing before starting and had a backup plan just in case. I just copied the set up from ACP and moved up to larger pumps and reservoirs. My set up is pretty much Stone Age tech. Now that a proper pump has been found the other 3 dozen issues need to be sorted out for a board to be made. Looking forward to the updates

Thats hooked up to the air pressure side correct? have you ever done any air brushing with it?

That’s the suck in side. Just turn on your pump and put you finger over the hole, you know instantaneously is its the blow or suck hole. The screw adjustment is to increase or decrease the suck or blow pressure.

I’ve air brushed with it. It works great. It nice cause you can dial the right air pressure for the material.

Interesting my vacuum or suck side is the right side on my machine.