Garlic Peeler

January 19th 2018

Objective

Deterime CFM requirements of Garlic Peeler.

Currently using a rented outdoor compressor. Problems

• Lines freeze
• Uses Diesel. Expensive to operate.
• expensive to rent
• requires maintenance

Query

What CFM compressor capacity is required to run the peeler?

Method

The system has 400 US gal storage tank. We used the tank to measure the cubic feet of air used. By filling the tank then turning the compressor off and measuring how long it took to drop to a given pressure we can determine many cubic feet we took out of the tank to run the peeler for a given time.

Measuring pressure in bar gives us an easy way to calculate cubic feet. 1 bar is atmospheric pressure (approx 14.5 psi). If we take 2 cubic feet of air and compress it into 1 cubic foot of space we have 2 bar (or 29 psi). If we take 3 cubic feet of air and compress it into 1 cubic ft of space the pressure is 3 bar (43.5 psi)

Based on the following assumptions.

• The storage tank is labeled at 400 us gal which is converted to a capacity of 53.5 cubic feet
• At 120 psi (8.2 bar) the tank contains 438 cubic feet of compressed air.

The following table shows the cubic feet of air released as the pressure drops from full (120 psi)

Tank Pressure	Tank Pressure Full	Tank Pressure	difference	tank volume	Cu.ft. consumed
120 psi	8.2 bar	1.0 bar	7.2 bar	53.5 cu.ft.	385.2 cu.ft.
98 psi	8.2 bar	6.75 bar	1.45 bar	53.5 cu.ft.	77.6 cu.ft.
94 psi	8.2 bar	6.48 bar	1.72 bar	53.5 cu.ft.	92 cu.ft.
93 psi	8.2 bar	6.4 bar	1.8 bar	53.5 cu.ft.	92 cu.ft.
90 psi	8.2 bar	6.2 bar	2.0 bar	53.5 cu.ft.	107 cu.ft.
87 psi	8.2 bar	6.0 bar	2.2 bar	53.5 cu.ft.	118 cu.ft.
82 psi	8.2 bar	5.65 bar	2.55 bar	53.5 cu.ft.	136 cu.ft.

Determine the output of indoor compressor

The indoor compressor takes 3.8 min to fill the tank from 90 psi to 120 psi. Therefore the measured capacity of the compressor is:

• capacity at 120 psi - capacity at 90 psi divided by the time to fill = cfm output of compressor
• (438-331.7)/3.8min = 28.0 CFM MEASURE OUTPUT OF COMPRESSOR FROM 90 TO 120 PSI

Determine the CFM consumed by Peeler

1. Filled the tank to max pressure 120 psi (8.2 bar)
2. Closed the feed to the tank so that no more air would be added. This gives us a Fixed amount of air to use.
3. Run the peeler for a fixed time at various pressures and recorded the pressure to drop.
4. From this data we calculated the CFM consumed at the preset pressures.
5. Calculate/measure the recovery time based on compressor capacity of 28 CFM.

Regulator Set	Start psi	end psi	cubic Feet	time	CFM	Refill Time	Recover 12 sec cycle
115 psi	120 psi	93 psi	96 cu.ft.	0.5 min	192 CFM	6.85 min	1.37 min
100 psi	120 psi	94 psi	92 cu.ft.	0.5 min	184 CFM	6.57 min	1.31 min
90 psi	120 psi	98 psi	77.6 cu.ft.	0.5 min	155 CFM	5.53 min	1.10 min
90 psi	120 psi	87.5 psi	116 cu.ft.	0.75 min	154 CFM	5.5 min	1.10 min
80 psi	120 psi	82 psi	136 cu.ft.	1.0 min	136 CFM	4.85 min	0.97 min

Conclusions

Based on the 28 CFM capacity of the indoor compressor, the cycle will need to pause to allow the compressor time to rebuild the pressure before the cycle can be repeated. We added a delay timer on the gate closed circuit to allow the process to be paused for an adjustable pause time between cycles.

FACTORS AFFECTING CFM CONSUMPTION

There are four adjustments that can be made to match the peeler to the capacity of the compressor.

1. Fill time -- if you change the amount of garlic per cycle it may change the time it takes to complete the cycle (peel all the garlic).
2. Cycle time -- The shorter the cycle the less air it will consume. If the cycle is too short and not all the garlic will be peeled. Too long will waste compressed air.
3. Pause time -- The time between cycles to wait for the compressor to build up pressure. The more air you use the longer it will take to recover.
4. Pressure -- the higher the pressure the more CFM will be consumed, (see the table above) varies between 136 CFM at 80 psi to 194 CFM at 120 psi. The longer it will take to rebuild the pressure.

Limitations

1. Only single tests were run with the exception of the 90 psi test that was run for 30 seconds and 45 second and gave similar results.
2. The higher psi tests ran to below the "design" pressure so the "true" CFM mas be higher if the the pressure is available.
3. These CFM values are for running continuously. The peeler typically runs for 12 to 15 seconds per cycle.