Gentlemen.
I have completed a York OBA setup on my rig, and I'm having some control issues. My setup is probably quite a bit different than the usual in that I designed it to perform both air down and air up tasks automatically, so please allow me to give a brief rundown of how it works before I get to the issues.
From the compressor, everything is as you'd see it anywhere else up to the check valve- copper line to deal with the heat, filter to pull the oil from the air, pressure relief valve, and finally the check valve. But downstream of that, I have a solenoid controlled dump valve that's used for airing down. The line crosses the top of the firewall and as it passes over the brake booster, there are two pressure switches tee'd in- one set to 16 PSI, and one set to 35 PSI. The line then goes down to the drivers side frame, tees off to run fore and aft to quick disconnects. On the male side of the QD, I have a tee with two ball valves and coiled hose that connects to the valve stems. On the electrical side, a repurposed rear heater fan switch sends power to the air up and air down components, depending on if I press "HI" or "LO." The HI and LO pressure switches are intended to allow the dump valve to release air during the airing down, and then once 16 PSI is reached, the LO pressure switch closes the dump valve. When I air up, the compressor fills the tires and once 35 PSI is reached, the HI pressure switch shuts off the compressor and actuates the pressure release valve to decompress the air line between the check valve and compressor outlet. Once I set the rear heater fan switch back to neutral, the entire system de-energizes and I can remove the tees and coiled hose from the QD and valve stems.
The problem I'm having is that while it all works as I intended, I'm having issues with pressure spikes causing the pressure switches to fluctuate. I attached a gauge to the system to see what was going on and during airing down, the LO pressure switch will close the dump valve when it reaches 16 PSI, but then there's a spike in the pressure, so the switch opens the dump valve again, reducing the pressure, causing the switch to close the valve again, ect ect ect... The same thing happens while airing up, but I suspect it's the pressure pulses from the compressor. When the pressure switches are electrically bypassed or if the system is more than 4 PSI away from the target pressure, it operates normally. The pressure spikes and subsequent feedback loops could best be described as sustained water hammer.
I'm going to install some pulsation dampeners between the pressure switches to see if that helps, but they're about a week out so I figured in the mean time, I'd post this up to see what you guys thought. Other solutions that came to mind were to move the pressure switches further away from the dump valve (currently, they're approximately 4' away), or add a two gallon tank to act as a surge tank and mount the pressure switches on that.
If there's interest, I can post pictures, schematics and do a full- blown writeup once I get things worked out. I will say this- with the pressure switches electrically bypassed, it airs down all four from 35 to 16 PSI in a little under two minutes, and airs them all up in a tick under three minutes... with the engine idling. It'd go faster if I used my hand throttle, but I haven't tried that yet.
I have completed a York OBA setup on my rig, and I'm having some control issues. My setup is probably quite a bit different than the usual in that I designed it to perform both air down and air up tasks automatically, so please allow me to give a brief rundown of how it works before I get to the issues.
From the compressor, everything is as you'd see it anywhere else up to the check valve- copper line to deal with the heat, filter to pull the oil from the air, pressure relief valve, and finally the check valve. But downstream of that, I have a solenoid controlled dump valve that's used for airing down. The line crosses the top of the firewall and as it passes over the brake booster, there are two pressure switches tee'd in- one set to 16 PSI, and one set to 35 PSI. The line then goes down to the drivers side frame, tees off to run fore and aft to quick disconnects. On the male side of the QD, I have a tee with two ball valves and coiled hose that connects to the valve stems. On the electrical side, a repurposed rear heater fan switch sends power to the air up and air down components, depending on if I press "HI" or "LO." The HI and LO pressure switches are intended to allow the dump valve to release air during the airing down, and then once 16 PSI is reached, the LO pressure switch closes the dump valve. When I air up, the compressor fills the tires and once 35 PSI is reached, the HI pressure switch shuts off the compressor and actuates the pressure release valve to decompress the air line between the check valve and compressor outlet. Once I set the rear heater fan switch back to neutral, the entire system de-energizes and I can remove the tees and coiled hose from the QD and valve stems.
The problem I'm having is that while it all works as I intended, I'm having issues with pressure spikes causing the pressure switches to fluctuate. I attached a gauge to the system to see what was going on and during airing down, the LO pressure switch will close the dump valve when it reaches 16 PSI, but then there's a spike in the pressure, so the switch opens the dump valve again, reducing the pressure, causing the switch to close the valve again, ect ect ect... The same thing happens while airing up, but I suspect it's the pressure pulses from the compressor. When the pressure switches are electrically bypassed or if the system is more than 4 PSI away from the target pressure, it operates normally. The pressure spikes and subsequent feedback loops could best be described as sustained water hammer.
I'm going to install some pulsation dampeners between the pressure switches to see if that helps, but they're about a week out so I figured in the mean time, I'd post this up to see what you guys thought. Other solutions that came to mind were to move the pressure switches further away from the dump valve (currently, they're approximately 4' away), or add a two gallon tank to act as a surge tank and mount the pressure switches on that.
If there's interest, I can post pictures, schematics and do a full- blown writeup once I get things worked out. I will say this- with the pressure switches electrically bypassed, it airs down all four from 35 to 16 PSI in a little under two minutes, and airs them all up in a tick under three minutes... with the engine idling. It'd go faster if I used my hand throttle, but I haven't tried that yet.
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