How many devices on a pigtail?

Boiler Talk

I see lots of folks putting several devices on one pigtail from the boiler.  Has anyone determined the amount of pressure lost from these setups?  Is it negligible?  Pressure loss is considered in creating pressurized systems No? 

DanHolohan

I think

One device is just right.

Hap_Hazzard

If you mean gauges and pressure-limiting devices

These devices don't cause any loss of pressure, unless they're defective. A gauge couldn't measure pressure very well if it allowed that pressure to escape.

Boiler Talk

I mean a gauge and a pressuretrol

I read your other comment on the other thread.  It makes sense to put a gauge on the pigtail with a controlling device.  I didn't study physics and I'd like to understand some of that stuff, but it seems to me the internet has pressure equations that cover pipes and fittings.  I'm probably making too much of this for 1/4" piping. 

Hap_Hazzard

Yup :-)

It's not really advanced physics. No relativity or quantum mechanics involved. It's mostly pre-Newtonian. Just picture how a gauge or pressuretrol works. Basically you have a diaphragm across a tube that is distorted by the pressure difference between the two sides. This diaphragm pushes a rod against a lever that turns a switch off and on again as the pressure rises and falls. A gauge works the same way, except the lever turns a gear that rotates the needle. (There are other types of gauges, but the basic principles are the same.)



While it's true that the distortion of the diaphragm results in an increase in the volume of the system, this change is only temporary, and it's insignificant on the scale of the system as a whole. It would be like worrying about how much heat is used up warning a thermometer when you stick it in a swimming pool.

Fizz

One is enough

Dan,



I will be adding a vaporstat to boiler, so no need for gauge or use separate pigtail?



Fizz

Rod

Splitting Pressure Controllers /Gauges

Hi-  If you use multiple gauges and multiple pressure controls (such as a vaporstat with the old pressuretrol as an extra high limit) it's a good idea to place them on separate pigtails.which are attached to separate boiler ports. With a gauge and pressure control combination on each of two pigtails/ports, if one boiler port/pigtail gets plugged up the other will still function. Also a difference between the normal reading of the gauges shows there is a problem developing.

- Rod

Boiler Talk

1 pressure control device and 1 gauge

I installed a gauge on the pigtail with the pressuretrol.   I don't have a vaporstat.  Thanks.