Crazy Idea....Pressure Triggered Time Delay

AdmiralYoda

My steam system has become quite the obsession! I'm thinking of making a time delay that is triggered by pressure and could use a bit of help from you guys that love controls.

My boiler is oversized and will cycle on pressure when its 20F or colder or if I use a setback. The radiators are screaming hot and full of steam when the boiler is at 3oz of pressure.

I'd really like to install a pressure switch that will trigger a time delay so the boiler will turn off for a period of time. This will allow the hot radiators to give off their heat without the boiler continuing to cycle. After this time delay if the t-stat is still calling for heat, the cycle starts over.

@PMJ mentioned a Dwyer 1900 series pressure switch and I think that would work great. The Macromatics TR series looks like a good time delay relay.

The problem I am having is most of the time delay relays usually apply voltage when a trigger is applied. I want the opposite, I want my boiler to turn off for a period of time when the pressure switch is triggered.

Any thoughts on how to make this work? This would eliminate short cycling due to pressure and should save me some fuel. The timing diagram below is how I want it to work.

EBEBRATT-Ed

You can buy all kinds of time delays. Delay on make, delay on break etc and there are others

AdmiralYoda

Yep..those are the ones.  Just having trouble finding one that will do exactly what I want.  I'm a controls noob.

ethicalpaul

Here's the one I use: https://www.amazon.com/gp/product/B08P53JFD1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I use the NC connection in series with the thermostat. The only bad part about this is that it triggers automatically when you power the device, so when you first power it up it opens the switch for one cycle. It's not a problem if you keep power on the device.

I use the Dwyer 1800 series low pressure switch to trigger mine. They come in a lot of ranges. I like the 1823-20 because it has a range of 3-20" WC. I have mine set at about 5" of water column. I set the timer for about 20 minutes (30% of one hour in terms of how the timer works)

https://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Switches/Series1800

I actually have a bunch of these extra of different ranges. Figure out what range you might be interested in and I can send you one.

This is the information that I was going to share with you in the other thread but I didn't get it together. Now that I know you are an EE guy I know I don't have to provide more information than this

AdmiralYoda

@ethicalpaul thank you!!!!

I don't power down my boiler often, just for routine maintenance and to install new gadgets so it shouldn't be a problem.

SuperJ

It's a good idea. I program building controls commercially and usually put a soft high limit control into my boiler programs. If the boiler hits it, its held off for at least 5 minutes maybe longer. Don't want a piece of equipment sitting there bouncing off a safety every couple seconds. If you have the interest/ability there a bunch of inexpensive fully programmable controllers you could use to trend a bunch of sensors and control your equipment. (note you shouldn't replace hardwired safeties with a programmble controller).

Here's nice one:
https://www.ccontrols.com/basautomation/baspiedge.php

AdmiralYoda

@ethicalpaul it looks like I would want the GRT8-A1. The timing diagram looks perfect.


@SuperJ That thing looks awesome! Might be a little overkill for what I need....but nice to know!

ethicalpaul

Honestly I have a hard time understanding this one. Let me know how it goes.

AdmiralYoda

@ethicalpaul The 1823-20 looks perfect!  I'll probably have the setpoint in the 5-7" range after some tinkering.

And we're you referring to the GTR8-A1 vs the B1? I like the A1 because it opens the T-Stat circuit when it senses a trigger signal.  In this case the trigger would be the Dwyer 1830-20.  The circuit stays open for whatever time I tell it to, then the circuit is closed and the boiler can fire back up if the T-Stat is still calling for heat.

ethicalpaul

Yeah I watched mine cycle a few times to see what the pressure was at different points. I recommend a nice Dwyer low pressure gauge to be able to monitor that and also to be able to set your 1800 accurately. I have a lot of extras of those also haha. I set mine with tubes connected to a Tee that I used my breath to pressurize.

AdmiralYoda

I've got an Ashcroft 0-20oz/0-35" gauge hooked up to the Vaporstat.  Should do the trick