Home Fire Sprinkler - how to fill?

Looking at an older house that has a fire sprinkler system in it but is showing 0 psi on the gauge.  
 

I haven't looked at it myself so I'm just fishing for some general info right now...   called a fire service and they are $985 just to come look at it and see if it will hold pressure.  Then it's $70/gallon for the appx 10 gallons of glycerine antifreeze the system requires. 
 

So of course I'm thinking, "Why can't I fix it?"  
 

but I can't find any videos showing how they get the glycerine into the system.   
 

so I'm wondering if anyone here is familiar with these systems and can give me a basic run down on why it might be showing no pressure with an apparently open supply valve as well as how to fill it with glycerine (that I found for $120/5 gallons) if it needs it. 
 

Before anything else I'd try a low pressure (10 PSI) compressed air test on it to see if there are any leaks.  Depending on age the sprinkler heads themselves may need to be changed, I know in the commercial world there were some made in the past that are a red flag when doing due diligence walkthroughs.  (I do HVAC but we work with the sprinkler fitters frequently.)

Be aware that your local codes will likely require a backflow prevention device between the glycol part of the system and any connection to the domestic water supply to prevent potential contamination of the domestic water system.  Older systems usually had a simple check valve which won't pass muster any more.  That may be why it was disconnected in the first place.

Also, some residential sprinkler systems are dry pipe and some are not.

You can do your own leak test with an air compressor and a Shrader valve, but other than trying to locate the leak to help them out, I recommend having a licensed pro do any repairs and updates.  They will sign off on the work.  If you do it and something happens, your homeowners' insurance will drop your claim (and your policy) with the quickness.

If you are going to use air pressure keep in mind that the pipe becomes a pipe bomb.  If the pipe is old and corroded it could rupture sending shards in any direction.

This is why industry hydro tests piping - any rupture and the pressure, and therefore energy in the system, goes to zero.  

So if you go the air pressure route keep the pressure low and spray the joints and pipe with soapy water to find leaks.  

 Can you educate me on the differences between hydro and air testing?  More for curiosity's sake.  Seems like if the system is pressurized to X psi, regardless of air or water, they could equally cause it to explode. 
 

Most homes in this area do not have sprinklers and they're not required nor expected for the loan so it's just a little project for me.

also, any suggestion on how to fill the system with glycerine?

jfryjfry said:

 Can you educate me on the differences between hydro and air testing?  More for curiosity's sake.  Seems like if the system is pressurized to X psi, regardless of air or water, they could equally cause it to explode. 
 

Air is compressible, water is not.  When a pipe ruptures due to air pressure, there is a massive amount of force pushing outward on the failed section, throwing potentially deadly shrapnel.  When a pipe fails due to hydrostatic pressure, sploosh.

Edit:  https://www.mcaa.org/pca/wp-content/uploads/sites/3/2016/03/SE86PDF.pdf

In reply to jfryjfry :

In air testing, it's a large volume of compressed air, carrying a lot of potential energy.  In hydro  testing, most of the system is filled with water with only a small compressed air bubble providing pressure; there is much less potential energy in the system.

In reply to jfryjfry :

All of the above is why I suggested a low pressure / 10 PSI test to see if the piping is even intact.  Hydro testing is absolutely the way to go if higher pressures are needed.  

To answer the question; air is compressible, liquids are not.  If you have a failure with high pressure hydro testing once the pipe fails the pressure drops nearly instantly as opposed to compressed air at a similar pressure which will take a period of time to bleed down as the pressure drops.

Ah of course.  Makes sense.   I currently plan on finding out if there is pressure or not.  Maybe a broken gauge but I doubt it. 
 If it's empty, I'll apply low pressure to see if any leaks. 
 

if none or if I can fix the leaks, I'll need to fill it with glycerine.  Still not sure how that happens.   Also not sure how the system even works but I assume it's full of glycerine from the back flow valve down and when a sprinkler element breaks in a fire, then water flows through the valve, pushing the glycerine and then water out.  
so I'd imagine I can close the valve and fill with glycerine from the furthest point, bleeding each sprinkler until full, then turn the water on.  
 

but maybe it's more complicated than that and I'm grossly oversimplifying it!

who knows....   I haven't even looked at the system yet!

Let me start off by saying I know nothing about these sorts of fire suppression systems.

That said, I'm surprised to hear you say it gets filled with gylcerine because as far as I know that's flammable.  Not as bad as gasoline certainly, but not something I'd expect to want to spray onto a fire?

Am I missing something?

It seems there are at least two different chemistries for sprinkler system anti-freeze:  propylene glycol based and glycerine based.

https://noblecompany.com/products/fire-sprinkler/freeze-protection/

We air test stainless steel metal hoses to 70psi and it's scary how they bulge out and grow.

We hydrostatic test rubber hoses to 375psi and if it leaks it spits out water.

Im not familiar with anti-freeze systems much but Ive taken a few out of service in the early 2000's with the impression being that they were obsolete, maybe having something to do with anit-freeze hitting the ground is bad for the environment, who knows. Anyhow my experience is with commercial construction but to hear a house has a anti freeze system is kinda odd. Is it a loop for an out door port/shed or the whole house, is the system primarily in the attic? And how do you know its anti freeze? Does it have a fill cup? The point of having this would be for it not to freeze. Dry systems are more standard these days but I dont really run into anti freeze loops unless its a really old building with an outdoor covering that needs sprinkler coverage. Old Home Depots some time still have these in the awning right before you walk in. If you trace the pipe back inside by the registers you can usually find all the crazy looking valves with gauges and such.

First you want to identify where the main valve is and make sure its closed which Im sure it is already since it seems like its been out of service from some time but you need to know where it is and also the main drain. The gauge that gives the pressure reading should be on a three way valve, check to see if its closed cause that would cause a zero pressure reading, open if closed. If it appears to be bad replace by closing the valve first then replace gauge and open valve once replaced. I f the system is in service it will give a pressure reading. If it is out of service and we were asked to put it back in service we would do a blow back test, it will tell you if you have an open outlet or not. This will sound weird but it works and its simple. Remove a head, take a deep breath and blow into the sprinkler head outlet and keep going to until your out of breath. Now if as soon you remove you mouth from the outlet and rush of air comes blowing back there are no open outlets (this is good) but it doesnt rule out possible leaks. If you blow and nothing comes back then you know you have an open outlet and you have to go around visually and look for a missing or broken head, cap, unfinished branch line etc. Word of warning though if you choose a low sprinkler head or one that is facing down on a extended pipe facing down (there called drops) then have a bucket or buckets ready to catch all that trapped anti freeze, in a house its probably not much. It would be best to find an upright head thats on top of a branch line to avoid any mess.

If we got good blow back then we go for air to find any leaks, you pump the system up to about 25-30 psi with an air compressor and see if it holds air, the goal is to have the gauge not move at all for at least 20 minutes. If its dropping then you have to go around and listen for air leaking. Now this can get tricky if your in a loud construction site and are dealing with a very large system. Some times we use mint oil in the pipe to sniff out the leak, spray bottle the fittings with soap and water and if it gets real hard to find we would start to section out the system by capping off sections to narrow down the leak. In your case you probably wont have any background noise blocking any hissing sounds. Once you find it, repair and if it holds air then you go for water.  Systems we work on have to hold fire pump pressure of around 130- 150 psi for one hour. Some buildings don't require fire pumps but still get tested at that pressure because it will see that pressure when the fire truck connects to the building via the FDC ( fire department connection).

Im not sure how residential gets tested so you should contact a local contractor for that info. As matter of fact I would recommend having a shop handle this type of work regardless because in my opinion it truly isn't a diy job. In the commercial field the inspectors that pass or fail you deal directly with Sprinkler companies and general contractors, we perform the hydro test right in front of them and I can only assume if someone other then a qualified Sprinkler fitter from a certified company performs the test they would walk away.

One last thing, from what Ive heard sometimes sprinkler systems in homes can do more harm then good, If its not monitored and a defective head goes off or an improperly installed joint burst then the home will get flooded until someone shuts it off. If no one is present at the home this could go on for hours. Although Im going to take a wild guess that any home with a sprinkler system especially a modern home is monitored  by an alarm company that will send an emergency call to the FD and they will come put out the fire if there is one and turn off sprinkler system when all is safe. In short its imperative to have your system monitored. 

and one more, one more last thing lol (sorry if Im nerding out here), sprinkler systems are not meant to save your home. They "suppress" the fire to give people enough time to get out of the house or building. Thats why there called Fire Suppression Systems. I think sometimes people get the wrong impression that it saves your home or building when in reality you will have fire damage and water damage on top of that.