A while back on the recommendation of jancumps I purchased a ZD-985 Desoldering station. I have been extremely happy with this purchase and even contracted with the vendor to upgrade their basic Chinese translated owners manual. There has, however, been one serious problem in the operation of the unit. To produce the vacuum that sucks away the solder it has a small internal vacuum pump that sounds like a small jack hammer. Every time I clear a solder pad it is BRAAAPT, BRAAAPT, and so on. During the day this is ok but since I do most of my work in the shop after the boss turns in I have to avoid the BRAAAPT. Here is a short demonstration of the problem .





                                             ZD-985 Desoldering Unit



Over the months since my purchase a solution to this problem has been taking shape and this last weekend I pulled all the parts together and Hacked the ZD-985 into a unit without the internal vacuum pump. Here are the parts that were needed and how they were put together. The first order was to locate an external vacuum unit that was quiet. For this I chose an old dehumidifier compressor that was still in good working order.




A test of the unit showed it was capable of producing a vacuum of 680 mm of mercury. The internal vacuum pump of the ZD-985 produces a vacuum in the range of 400 mm of Hg so the external vacuum would be a nice improvement. I was aware that the unit would have to be lubricated periodically as the original lubricant was the refrigerant and this of course was no longer in the system. An enternal oil port would have to be provided. It would also be necessary to add some vacuum storage capacity to the system so that there would be some depth to the vacuum when needed. Another feature would be a gauge to read the level of vacuum in the system. Finally, an electrically controlled pneumatic solenoid would be needed so that the vacuum would be available to the desoldering handpiece on demand. A list was made and a field trip to son Matt's Dental Equipment Repair Shop was planned to scavenge the parts. Before leaving however it was important to determine what space and voltages would be available inside the ZD-985.




The cylinder with the test leads attached is the motor that powers the internal vacuum pump. When powered it showed a DC voltage of approximately 12 volts. This pump would be removed and it is apparent that there will be plenty of room for a pneumatic solenoid and at this point I knew that the coil would have to be 12 VDC. There would also have to be room for a relay in the ZD-985 as it was important that the external vacuum be switched on with the power switch on the ZD-985. For this a small 120VAC relay would be powered off the units main power switch and the relay contacts would then be used as a switch for the external vacuum.

Here is a picture of the ZD-985 with the internal Vacuum pump removed. The red wires visible around the power supply are the switched 120 VAC power wires and where the relay would be tied later in the process.




After a trip to Matt's Dental Shop I returned with the following parts and pieces as well as vacuum tubing used for dental saliva ejectors and some fittings to tie them together.




These are 2 liter water bottles that are designed to withstand 400 or 500 kPa of positive pressure. The vacuum of 680 mm of Hg would not collapse their sturdy construction. These will serve as the vacuum reservoir.




The system vacuum gauge is marked in Inches of Hg but this is a system that is very familiar here in the US so it will be comfortable for me to use.



The solenoid has a 12 VDC activation coil and the internal valve orifice is about 4 mm. This is important because the negative pressures involved in working with vacuum are really quite low and too small of a  diameter valve seat would result in resistance that would impeded the flow of air. The next step in the process is the fun part, assembly.




Here is the assembled vacuum unit tucked under the bench and out of sight. You can see the bottoms of the two bottles that are serving as a vacuum reservoir. There is also a glass jelly jar on the right side that is being used as a reservoir for the oil as it comes from the exhaust. As part of routine maintenance oil will be eye dropped into the vacuum input of the pump and this oil will lubricate the pump and eventually be blown out in the exhaust. The jar will catch the oil so it doesn't get all over the floor and shelving. From the pump the vacuum line hose goes up to the ZD-985 and the Vacuum Gauge which I have mounted on the shelf along side the desoldering station.




In this picture we can see the solenoid mounted inside the ZD-985 and the vacuum pump relay mounted to the right. The power that originally ran the internal 12 volt pump motor now powers the solenoid. I have also wired a flyback diode across the solenoid coil to protect the circuit. Vacuum hose has been run from the solenoid to the front vacuum adapter of the ZD-985 and another piece out the back of the unit. It is not necessary to clamp or strap the hoses to the barbs as the negative pressure in the system will keep the seals tight.




The back of the reassembled unit with the relay switched line and the vacuum hose showing. The unit was now connected to the external vacuum pump and the gauge and a test was run to see if everything was performing as hoped. Here is a short video of the unit and what it sounds like during operation.



Thanks John