Manometer for measuring boiler pressure

SteamingatMohawk

I just had an "brainstorm". I have a manometer I use to check the gas valve outlet pressure. I do not leave it connected.

I just wondered if anyone has ever use this type of device to check how high the steam pressure goes. Then it would be easier to determine which really low pressure gauge to get, if someone wanted to get something like a Magnehelic.

KC_Jones

@ChrisJ @ethicalpaul have Magnehelic installed and I have one on the shelf waiting for me to get the time to hook it up.

ethicalpaul

KC means the gauges.

as for a manometer, yes it would work fine but if your pressure goes higher than your meter, it will push water out the top.

so I’d only use it for a fun experiment or put a valve on it for when it’s not attended.

but you don’t really need it, just get a gauge that has a range of whatever psi you see.

like if you have a 0-3psi gauge and you see it go to 1/2 psi then get a magnahelic with a range of like 20 inches of water column

ChrisJ

https://youtu.be/hH36luC9GKU

Connected directly into the boiler, no pigtail just an 18" tall 1/2" steel vertical pipe as an air gap.

Air can't get out so steam can't get in.

Pigtails cause issues when measuring pressure this low because of the weight of the water etc.

neilc

I have clear(was) vinyl tube, on a hose end repair, attached to the boiler drain,
the tube is long enough to reach up over pipe at the ceiling, and back down to about 6 inches to the floor for safety,
I don't leave the drain open when I'm not there,
measures inches of water above normal water line real well.

mattmia2

Dwyer makes some electronic gauges that have both high precision and a fairly wide range which I think could measure the tiny pressure of an open system venting and the possible 2 or 3 psig of a system with a presduretroll shutting down on pressure.

mattmia2

Thinking some more, couldn't a thermostat attached to the hx below the water line act as a tertiary protection against dry firing?

ethicalpaul

Sure could. Like the thermal fuse they put in the windings of mixer motors (and probably lots of other motors)

ChrisJ

A Magnehelic is safe up to something like 16 or 20 psig.

It'll only register up to a few inches but won't be damaged by going higher 

ethicalpaul

ChrisJ said:

A Magnehelic is safe up to something like 16 or 20 psig.

It'll only register up to a few inches but won't be damaged by going higher 

Yeah and the newer ones have a blowout plug that will...blow out if you over-pressurize it

SteamingatMohawk

@mattmia2 Connect the dots for me...how does your comment about a thermostat have something to do with using a manometer to check boiler pressure?

@neilc That's quite a MANometer! LOL

mattmia2

I think it came from we control a steam boiler on pressure(and a failed pressure control could damage your measuring device) and then we control it with a low water cutout which both are somewhat complex and have rather common failure modes that can cause them to fail closed and that a block of cast iron full of water won't get hotter than the water so a thermostat (or thermal fuse as @ethicalpaul suggested) is a lot less prone to failing to shut the burner down.

SteamingatMohawk

Thanks

GBC_illinois

SteamingatMohawk said:

I just had an "brainstorm". I have a manometer I use to check the gas valve outlet pressure. I do not leave it connected.

I just wondered if anyone has ever use this type of device to check how high the steam pressure goes. Then it would be easier to determine which really low pressure gauge to get, if someone wanted to get something like a Magnehelic.

I have done this, because even though I have a low pressure gauge (32" WC), it acts up and I don't trust it. To make a simple manometer, I connected a silicone tube to the sight glass drain. As long as you are running at low pressures, like under 1.5 psi, its easy. Here are some pics of my setup. Note that the marks I made are in oz of pressure, not inches of water.

SteamingatMohawk

I just saw your comment, sorry for not looking sooner.

Nice.

EBEBRATT-Ed

The old garden hose trick

Hap_Hazzard

ChrisJ said:

Air can't get out so steam can't get in.

Maybe I'm not understanding what you described, but in a ½" pipe, the steam could rise right through the air, couldn't it?

ChrisJ

Hap_Hazzard said:

ChrisJ said:

Air can't get out so steam can't get in.

Maybe I'm not understanding what you described, but in a ½" pipe, the steam could rise right through the air, couldn't it?

In order for steam to rise through the air some air would need to be pushed out.
The air will not push out as the entire opening of the 1/2" pipe is exposed to the same pressure.

109A_5

Hello @Hap_Hazzard,

Hap_Hazzard said:

ChrisJ said:

Air can't get out so steam can't get in.

Maybe I'm not understanding what you described, but in a ½" pipe, the steam could rise right through the air, couldn't it?

Seems maybe a bit counter intuitive. I have a 12" long 1/4" pipe (above the boiler jacket, out of the top of the boiler) with trapped air. About 8" up I can hold my fingers on it for the whole boiler run. 8" up on the 2" Steam main I will get burned. So yes it does seem where air is stagnant (or trapped) Steam won't go. I suspect where the Steam meats the air it cools enough that it then becomes condensate and propagates no more (as Steam). Clear tubing experiments are fun, don't get burned.