- Getting the material
- Building instructions
- The final result
- Tips for using your vacuum press
What the hell a step-by-step instruction to build a vacuum pump is doing on a site dedicated to the electric helicopter?...
I must admit that it may sound strange, but I will list you some application that may bother the heli pilot you are. For example, you may use it when building your own self-made canopy, a new composite undercarriage or a set of custom blade. In fact everytime you will need to press something for quite a long time.
This is often the case when you work on something using composite (such as carbon fiber, glass fiber tissue, Kevlar,...), you always need to press the different layer on a shape and keep them in place in order to let the epoxy polymerise.
People often use heavy loads, sand bags, their collections of magazines or anything in the neighboourhood looking heavy but they never obtain a regular and optimal pressure on all parts of the work. By using vacuum, you can apply the same high pressure on all parts. How can this be achieved?... Answer: by using athmospheric pressure! All you need to do is put your items inside a polyethylene plastic bag and use a vacuum pump to lower the pression inside the bag.
A depressure of -100 mbar gives a load of 100 kg per square meter, if you apply -500 mbar, you will end up pressing 1/2 ton per square meter. Our problem now is to get a vacuum pump and a regulation to do it. You can find some on the market but at a retail price that will make you think twice before buying it. Other solution is to build your own. The solution I will describe here has been validated and I will explain you how to build it for almost nothing.
You will be dealing with current, so be careful
Getting the material
In order to build your own vaccum pump you will need the following items:
One fridge compressor unitFig.1 Fridge compressor unit
Go to your local fridge resselers, they often offer to take the previous back when customer buy a new one. And they dont know what to do with them. Ask them if you cannot take one off. You will need a good cuting plier to cut in and out tubes. Please avoid using a metal saw to cut them because the metal dust can enter the tubes and give trouble later.NoteTake care to let at least 10 cm of in and out tubing. Pay attention while handling the compressor they are often filled with oil. You must keep it inside. press the last centimeter of the tube to seal it for transport
One admission advance regulation valve OR one glass syringe
This part can be found in almost all old engine (with no electronic advance regulation). This looks like a metallic can like a flying saucer with a tube on top.(crazy definition but I do not engineered these parts anyway) How does it work? It contains a rubber membrane that can move depending on the depression applied at the inlet tube. The more depression there is, the more the membrane moves. An iron wire is linked to the center of the membrane and moves with it.Fig.2 Vacuum valve front viewFig.3 Vacuum valve side view
If you cannot find that part, you can go to your pharmacy and ask for a glass syringe (The bigger, The better). We can also use it for this job.NoteDo not use a plastic syringe, it is not up to the job.
One 220v. microswitch
It should be strong enough to support the load of the fridge compressor unit you have. Speak about this with your electronic part reseller.
One manometerFig.4 Fuel Pump Pressure vacuum manometer
You will find this item in any car supply store. It is used to check fuel pump aspiration. It as generally scaled from -1 bar to + 5 bar stepped by 0.1 bar. It is really low cost item.NoteThis item is optionnal, but is useful to precisely set the depression value you want to apply. When using foam core forms, you should not apply too much vacuum or the form will collapse on itself. (Max depression for foam core is -0.4 bar, if you apply more, deformation may occur ruining your work.) Always perform some experiments before in order to know the limit of your materials.
Some meters of plastic tubing
It should be strong enough not to squeeze on itself under vacuum.
A ping-pong ball
I bet you are wondering what we gonna do with this ...
to build the box around the regulation to protect user from electric shock.
One spring + nuts and bolts
you can canibalise one from a old camp bed or go to a outdoor shop to find spare ones.
One Bycicle wheel spoke
This will be used to replace the iron wire connection on the admission advance regulation valve. The original one is too short and the wheel spoke is threaded with the thread.
There's two regulations possible, one using the car part and the other one using a glass syringe. Here below you will find:
- detailed instructions to build the car part one with some photos. a
- basic instructions to build the syringe regulation
Building the Car part based regulation
Understanding the principleFig.5 Car part regulation principle
The principle is easy to understand. When connected, the compressor will turn ON and begin pumping. As more and more vacuum is applied to the inlet of the valve, the iron wire moves back releasing pression on the micro switch. When the OFF position is reached , the compressor unit stops. Due to unavoidable leaks, the vacuum will lower little by little and the iron wire will come back pushing the microswitch ON, starting the compressor unit for a new cycle. The more the bolt retaining the spring is tightened, the more vacuum depression you will get.
Build a wooden box out of plywood in order to put all hazardous parts inside a secured area. Install the valve outside just letting the iron wire go inside. Bolt the microswitch to the base and connect the power wires to it (soldering is just fine). All you need is to install the bolt and spring and connect it to the iron wire coming from the valve. solder a push button guided to the switch by two piece of wood. Job is done...Fig.6 Car part regulation exampleFig.7 Car part regulation bolt
Install your electric junctions in an isolated box on top of your wooden box. This will be easier for later maintenance.Fig.8 Car part regulation overview
Syringe based regulation
Understanding the principleFig.6 Syringe regulation principle
Principle is not very different from the car part based solution. The only limit here is that the system MUST be fixed verticaly and firmly attached due to the load. When connected, the compressor will turn ON and begin pumping. As more and more vacuum is applied to the inlet of the syringe, the piston moves up releasing pression on the micro switch. When the OFF position is reached , the compressor unit stops. Due to unavoidable leaks, the vacuum will lower little by little and the piston will come back due to the load in the basket pushing the microswitch ON, and starting the compressor unit for a new cycle. The more load in the basket, the more vacuum depression you will get.
To build this regulation, take care to fix the syringe firmly. It is best to fix it using collars (like tie-raps) over small strip of rubber cutted out of bycicle wheel tubes. Be careful not to brake your syringe. Take care to limit the piston move with one or two nails. It should only be able to move until the switch is fully pressed ON, not lower in order to avoid mechanical load on the switch.
Installing your fridge compressor
- You should firmly install your fridge compressor on a wooden plate using the rubber damper you found when dismanteling it.
- Normally you shoud have let 10 cm of tubing. The last centimeter flattened for transport. We can now cut the in and out tubes in a proper way. Use a tube cuting tool to shorten them to 8cm.
- Identify the IN and OUT tubes by starting the compressor.
WarningSome oil may be projected by the OUT tubes so keep yourself out of the way.
- On the OUT tube, fix a 20 cm tube. Guide this tube verticaly on a wood stick and cover the end with the ping-pong ball. drill small holes in the ball so that the air can get out. This little ball will act as an oil recuperator.
Fig.6 Ping-Pong ball installation
- To the IN of the compressor you will fix the vacuum tube. On this tube you will add a "T" in order to get one tube to go to the inlet of the regulation and the other one to the bag. Optionaly you may add an other "T" to be able to add the manometer in the chain. But it can be a new source of leaks.
Fig.6 Tube installation
- Now seal all links using silicone and tie-raps. Let dry...
- Proceed with the few tests. You should be able to fix most of the problem by yourself. if not, you can go to the Ikarus Eco8 forum and post your trouble.
The final result
If you have choosen to go for the Car Part version, you will end up with something looking like this:
Fig.6 Vacuum pump - lateral view
Fig.6 Vacuum pump - top view
Fig.6 Vacuum pump - front view
Tips for using your vacuum press
- Use only polyethylene plastic, this material cannot be glued using common epoxy glues. You will find this very useful when time to open bag will come.
- I use silicone to seal my bags. Others use window mastic but it is not as good.
- Sometimes, the plastic of the bag covers competely the pump tube thus stopping pump too soon. In order to avoid this case, here's a simple trick. Use a large wool string that you install all the way round your work inside the bag and put one of its end inside the vacuum tube. This will act as a air drain and will insure optimal depression repartition inside the bag
- Listen carefully to your bag sealing to detect leaks. You should track them to avoid unnecessary pumping.
- Most fridge compressor got a overheating protection, if it starts too often in a short period the motor may fall in secure mode. You will have to wait until relay cools down with cord unplugged from outlet.