Manometer experiment

Fred Harwood_2

You can make one by fitting a clear plastic tube to a hose bib barb, and screwing it onto the boiler drain, for example. The boiler pressure will raise the water in the tube 28 inches for each psi.

Don't leave it alone ...

David Nadle

Manometer experiment

A million thanks to whoever suggested using a manometer to check your pressure gauge. I rigged one up out of some tubing and a meterstick and connected it to the drain at the bottom of the equalizer. I believe I have a plugged pigtail. This is the boiler's second season and if I'm right the pigtail must have been plugged shortly after the boiler was installed. I never expected that to happen so soon.

All this time my digital gauge was reading way low; about 2 ounces. I figured that was the pressure and that's why the vaporstat at 6 ounces was never breaking contact. The manometer has proven me wrong. I am operating at 8 ounces and up -- at 1.6 PSI i had to shut the drain valve because the water was about to hit the ceiling. And the boiler was still firing. I attached a plot.

I've got a new pigtail coming tomorrow. I'll report back what I find if anyone's interested.

Norm Harvey

I may have missed the suggestion, but what are you checking with the manometer and whats the set up like?

Do you have any photos?


Also,.. just FYI,.. I am a ten on the man-o-meter.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Unknown

I'll report back what I find if anyone's interested.

Are you kidding?, sure we`d like to know.
Good show David!!
Kudos on your ingenuity!

BTW- Great name.

Dave

Norm Harvey

That is awesome! I'm going to make one of those right now !

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

David Nadle

Duly noted...

Your masculinity was never in doubt.

I could post a pic but it's really simple to explain. A garden hose to barbed tubing adapter, about 8 feet of 3/8" flexible tubing, a few hose clamps, and a meterstick.

The hose end is screwed into the drain teed into the bottom of the equalizer. The other end is clamped to a hook and hung from a water pipe running just below the ceiling joists. There's enough slack so the tubing looks like a J. The drain valve is opened and the waterline finds equilibrium in the hanging part of the tubing. The meterstick is taped to the tubing so that the "off" waterline is at or near the meterstick zero.

As the boiler steams the water column in the tubing rises, measuring pressure in cm or inches of H20. 1 PSI is 28 inches of water. In my basement that means you can't measure above 1.6 PSI or so.

The waterline bounces around a bit, that's what the error bars represent on the plot. But for about ten bucks in parts you have a way to check gauges and vaporstat settings. I'm pretty sure I'm going to find a plugged pigtail when I remove it this weekend.

johnnyge

Post pict.of the manometer and how did you installed it

Unknown

You can do the same thing

by removing the plug on the McDonnell Miller 67 low water cut off with a 1/4" nipple and a manometer a lot easier, been doing it for years.

David Nadle

Good idea, but I have a probe type LWCO.

I disassembled the contraption earlier, but I'll hook it up again and post a pic on Saturday.

David Nadle

Update -- and questions

The pigtail was plugged. After replacing it I hooked up the manometer again to check the gauge and vaporstat. I attached pics of the manometer rig and a plot of the observed data.

The vaporstat was set to 9 oz cut out, 3 oz cut in based on the knee in the curve found in the first manometer run. The vaporstat broke contact at 9.5-10 oz, not too bad.

But...the pressure did not hold. It fluttered around 5 oz while the boil ceased, then plunged to about 2 oz vacuum for a bit. The vaporstat made contact again and the burner was igniting within 40 seconds. Then within another 40 seconds the vaporstat was cutting out again.

The system continued this 40 seconds on, 40 seconds off cycle until the thermostat was satisfied. I can't imagine this is ideal.

David Nadle

Update -- and questions

The pigtail was plugged. After replacing it I hooked up the manometer again to check the gauge and vaporstat. I attached pics of the manometer rig and a plot of the observed data.

The vaporstat was set to 9 oz cut out, 3 oz cut in based on the knee in the curve found in the first manometer run. The vaporstat broke contact at 9.5-10 oz, not too bad.

But...the pressure did not hold. It fluttered around 5 oz while the boil ceased, then plunged to about 2 oz vacuum for a bit. The vaporstat made contact again and the burner was igniting within 40 seconds. Then within another 40 seconds the vaporstat was cutting out again.

The system continued this 40 seconds on, 40 seconds off cycle until the thermostat was satisfied. I can't imagine this is ideal. I figure I have two options. One is to hunt around for any vents that may have been damaged by the overpressure from operating with a plugged pigtail and replace them in hopes of holding pressure longer.

The other option is to add an on-delay relay to the vaporstat circuit, to set some minimum off time, like 5 minutes or so. This would give the condensate more time to return to the boiler and take advantage of the thermal inertia in the rads.

I'd love to read your thoughts on this.

Fred Harwood_2

manometer test

Your runtime sounds too long. What thermostat are you using, and can you set it for two cycles per hour?

David Nadle

It's a VisionPro set to 1 CPH.

Fred Harwood_2

Cycles per hour

Try two cycles per hour.

David Nadle

Could you elaborate?

Fred,

My understanding of the CPH setting is it doesn't limit run time but limits the number of cycle starts per hour. I can't see how changing the CPH setting is going to help.

Fred Harwood_2

Cycles per hour

Steam systems are prone to overshooting the set temperature. Few steam systems should heat the rads all the way across and close the rad vents on each cycle. Rather, only on "design day" (really cold) should the rads fill.
So you want your thermostat to sample room temp at least twice an hour so that it doesn't overshoot, then cool back, then overshoot, etc.
If you can set your thermostat for two cycles per hour, try it. It might stop your short cycling against pressure.

Howard Emerson

Every time I hear that word............

............I can not help but hear THIS in my head:

http://www.youtube.com/watch?v=_7V5Qh7Wke8

Please forgive me, or show it to your kids:-)

HE

David Nadle

The thermostat is certainly sampling more often than once an hour. On a warm day my system might run for 5 minutes. The thermostat is limiting runtime, not the CPH setting. I think you have a fundamental misunderstanding of how CPH setting affects operation, or I do.

David Nadle

Awesome. I remember that well. And I will show it to my kid.

Fred Harwood_2

Cycles per hour

I don't know your thermostat, and I thought you said that the boiler is short-cycling after it runs for more than a half hour, which sounded like a very long time for a boiler to run on one cycle, unless the thermostat has been set back.
For example, steady state, 14F outside, my T87 runs the boiler for about 6 minutes in each 25 or so. No overshoots, no cold rooms, no cycling on the Vaporstat.

David Nadle

The pressure reached 9 ounces after 40 minutes. The vaporstat shut off the boiler, but the pressure dropped to zero within a minute and so the boiler ignited again.

On a normal run with a low heating load the thermostat would have been satisfied before the vaporstat and the run time would have been shorter.

I made no complaints about overshoot or cold rooms, and I have none. My question concerns what to do about the condition when the vaporstat is breaking contact but the pressure does not hold, and I don't beleive any thermostat can address that.