I purchased a number of automatic vent openers for my greenhouse. These vent openers have cylinders that are filled with a paraffin. When warmed, the paraffin expands and contracts when cooled. This movement pushes a plunger in and out. The out movement will push a vent open and the contraction is supposed to close the vent. But... there is a design problem. When the plunger contracts, it has to pull the vent closed against gravity. It needs to lift the vent as well as close it. This means that the vents don't close tightly. Tight closing is essential to conserving heat. The design of the openers doesn't permit turning them around since the cylinder would be in the soil. I needed to redesign the openers so the would work with gravity.
Step 1: Design Problems
The existing vent openers need to be fastened opposite the vent hinges. If reversed, the cylinder will be in the soil and will not work. I needed to arrange the vent openers so they fell on the same side as the hinges of the vent.
Step 2: Design Solution
Using the extension of the plunger to push the vent open could be accomplished by pushing on a bracket that was attached to the vent.
The cylinder needs to be able to rotate over an angle that accommodates the rotation of the bracket around the hinge. The distance between the bracket and hinge should be roughly equal to the range of movement of the plunger in the cylinder.
- 18 gauge galvanized sheet metal for bracket
- aluminum1 1/4" tubular
- 1/2" machine screws, with nuts and washers
- automatic vent opener
- 1/2" machine screws
- 1/8" nylon bushing
I cut the Al tubing at a 45 degree angle with 1/4 inch cut off the end. I then drilled holes to secure the housing on the frame of the greenhouse. I then drilled a 3/16 hole across the housing to hold the circular cylinder bracket.
Step 3: Building a New Vent Opener
The rearranged vent opener is then screwed onto the greenhouse frame on the same side as the hinge. The bracket is then screwed on the vent about 2" from the hinge. The vent opener is linked to the bracket with the plunger. When the opener warms and the plunger moves out, it pushes the vent open. When it cools, the vent closes with the help of gravity.
Cut small sections of nylon line to create a bushing for the machine screw where it passes through the holes in the Al housing. This is necessary to avoid corrosion of the Al from the steel threads.
Step 4: Installing the New Vent Opener
Screw the housing onto the greenhouse frame.
Screw the bracket onto the vent about 2" away from hinge.
Thread the cylinder in or out to adjust the opening temperature.