“This is a Veneer Vacuum Press (Vacuum Pump) which has been modified with a Digital Vacuum Regulator to operate with a selectable vacuum pressure. This device is a replacement for the Vacuum Controller in my DIY Veneer Vacuum Press built with plans from VeneerSupplies.com or JoeWoodworking.com. These are great plans and the pumps operate very satisfactorily as designed. However, I’m a tinkerer, and I wanted to enhance my pump with the ability to easily and readily control the pressure settings (without a screw driver) over a wider range of pressures with a digitally controlled regulator.
Recently, a need arose which was beyond the lower limits of my Vacuum Controller (Type 1). This project required a Type 2-Vacuum Controller for pressures in the range of 2 to 10 in-Hg. Replacing my Type 1-Vacuum Controller with a Type 2 model was an option, however, this seemed impractical since it would require an additional cost and modifications to switch between the two vacuum ranges. The ideal solution is a single controller with a wider range of pressures (2 to 28 in-Hg).
Vacuum Controller: A vacuum controlled micro-switch used to activate a vacuum pump or relay at a selected pressure. The vacuum controller has an adjustment screw that allows you to dial in your desired level of vacuum. The contacts are rated at 10 amps at 120v AC.
Types of Vacuum Controller:
Type 1 = adjustable for 10.5” to 28” of Hg (Differential 2 to 5” of Hg)
Type 2 = adjustable for 2” to 10” of Hg (Differential 2 to 4” of Hg)
My design replaces the Vacuum Controller with a Digital Vacuum Regulator (DVR). The DVR will be used to control the LINE-DVR line of the RELAY-30A as seen in the Main Control Box schematic. This design requires the addition of a AC/DC 5-VDC Power Supply to Main Control Box for powering the DVR.
This design is capable of maintaining a wide range of vacuum pressures, but the performance is entirely dependent upon the capability of the pump. At the lower pressure range a large CFM pump will maintain these pressures, but result in larger differential pressure swings as a result of the displacement of the pump. This is the case for my 3 CFM pump. It is capable of maintaining 3 in-Hg, but the differential pressure swing is ±1 in-Hg, and the ON cycles of the pump, although infrequent, last approximately one or two seconds. A differential pressure swing of ±1 in-Hg will result with pressures between 141 lbs/ft² to 283 lbs/ft². I have no experience vacuum pressing at these low pressures, therefore I am not sure of the significance of this differential pressure swing. In my opinion, a smaller CFM vacuum pump would probably be more appropriate to maintain these lower vacuum pressures and reduce the differential pressure swings.
The construction of this regulator includes a Raspberry Pi Zero, MD-PS002 Pressure Sensor, HX711 Wheatstone Bridge Amplifier Module, LCD Display, 5V Power Supply, Rotary Encoder and a Relay Module. All of these parts are available from your favorite internet electronics parts suppliers.
I choose a Raspberry Pi (RPi) because python is my preferred programming language, and the support for RPi’s is readily available. I am confident this application could be ported to an ESP8266 or other controllers capable of running python. The one disadvantage of the RPi is a Shutdown is highly recommended before powering it down to prevent corruption of the SD Card.
PARTS:
1ea Raspberry Pi Zero - Version 1.3 $5
1ea MD-PS002 Vacuum Sensor Absolute Pressure Sensor $1.75
1ea HX711 Load Cell and Pressure sensor 24 bit AD module $0.75
1ea KY-040 Rotary Encoder Module $1
1ea 5V 1.5A 7.5W Switch Power Module 220V AC-DC Step Down Module $2.56
1ea 2004 20x4 Character LCD Display Module $4.02
1ea 5V 1-Channel Optocoupler Relay Module $0.99
1ea Adafruit Perma-Proto Half-sized Breadboard PCB $4.50
1ea 2N2222A NPN Transistor $0.09
2ea 10K Resistors
1ea Hose Barb Adapter 1/4” ID x 1/4” FIP $3.11
1ea Brass Pipe Square Head Plug 1/4” MIP $2.96
1ea GX12-2 2 Pin Diameter 12mm Male & Female Wire
Panel Connector Circular Screw Type Electrical Connector Socket Plug $0.67
1ea Proto Box (or 3D Printed)”