Geyser question(boiler)

[PlumbSolve]

I am amazed at how different your plumbing is to my country.99 % of all geysers are electric in S Africa. Our system is very simple. We install a PRV at the entrance to the house in order to balance the entire system. These PRV,s are rated at 4 or 6 bar.(don't know what that is in psi.)It has a built in pressure relief valve . Our geysers are then mounted in the roof under a drip tray and there is a pipe to the outside which is connected to the temperature and pressure valve. Our PRV leak when water is heated so it normally discharges over a drain. I keep hearing about an expansion tank. What is this expansion tank and how does it work.? Is it doing the same role as our relief valves.?

 

[Terry]

An expansion tank has a rubber bladder to hold water, with an air charge behind it. When the water heats up and expands, it compresses the air behind the bladder, and the bladder takes on more water.
We install these when there is a closed system, like a check valve at the meters. I also install them if I know there is a PRV on the system.
There are some PRV's that have a pressure bypass on them.

 

[Sponsor]

 

[PlumbSolve]

An expansion tank has a rubber bladder to hold water, with an air charge behind it. When the water heats up and expands, it compresses the air behind the bladder, and the bladder takes on more water.
We install these when there is a closed system, like a check valve at the meters. I also install them if I know there is a PRV on the system.
There are some PRV's that have a pressure bypass on them.

When you say a closed system are you referring to a boiler that is pressurized and not open to atmospheric pressure such as a combination system(gravity geyser.)?Then how much would the bladder be pumped up to? I am trying to my get my head around this . If the geyser is set at 60 Celsius and you use some hot water the element will then kick in and heat the water. Because its a closed system hot water expands ,does this expansion land up in the tank.? How do you know the tank is big enough to do the job? and if the tank loses pressure and needs to be repumped or replaced what would happen to the expansion. Would it not stress the geyser before its found out.? Also if the tank fails would it not flood the place? What I am not understanding is that if your PRV is set at 6 bar surely the tank bladder would have to be greater in pressure or wouldn't the bladder be filled up with water at that pressure.?
Hope I don't get flack(Might be asked to go get my license) for asking dumb questions but the reason for my questions is that we are bound by very strict laws in terms of geysers and its a criminal offence to install it incorrectly. Our biggest problems in flats is what to do with the constant expansion going down the drain. A bladder may resolve that problem

 

[PlumbSolve]

okay I got it. I just assumed the expansion tank is prepumped lower than the street pressure. We use these expansion tanks on booster pumps to prevent the motor switching on and off excessively. They are pre pressurized to 1.5 bar. I watched a couple of u tube videos and now understand it.
But for the life of me I cant understand why you don't just use a built in relief on the PRV. Its so much cheaper, takes less space and seldom fails and there is hardly any risk if it fails as it wont flood a place.
Is there a reason for it.?
I can think of one .I suppose on a planet with water becoming a scarce commodity this would prevent water from just being dumped. Also fly by night plumbers plumb these expansion pipes directly into the waste pipes by simply drilling a hole in the 4 inch stack and using some pex pipe into the sewer. If its faulty the home owner could never even know he is wasting water. If you add up millions of households dumping water into drains it would add up. Is this the reason for using expansion tanks. I am curious to know.

 

[Reach4]

my country.99 % of all geysers are electric in S Africa.

I think you are talking about what we would call a water heater.

We call the things that make heat for hydronic heating systems boilers. Those would often have thermal expansion tanks also.

 

[PlumbSolve]

Why do you you a bladder tank system instead of a simple and much cheaper pressure relief valve? I would be curious to know why?

 

[Sylvan]

Why do you you a bladder tank system instead of a simple and much cheaper pressure relief valve? I would be curious to know why?

NYC is blessed with a gravity system installed in the late 1800's whch supplies several billions of gallons of water a day

Because it is a gravity feed system the majority of applications have a water pressure under 60 PSI (BAR 4.13685)

The only time I needed to install a PRV was by either a pumping station or a high rise building 47 stories in height for example

The Code stated water pressure exceeding 85 PSI has to be reduced to 85 which is uncalled for in most applications (except fire suppression)

The problem with excessive pressure besides water hammer (hydraulic shock) is the velocity can exceed 8 FPS which can cause copper tubing to suffer from erosion not to mention the flooding from such high pressure

Hydronic boilers have a PRV set between 12- 15 PSI (0.827371 - 1.03421)

The reason being most of these boilers are installed in buildings less then 25 feet high

So taking 12 PSI x 2,31 = 27.72 feet and then we add a fudge factor to make sure there is positive pressure in the system

The water used to fill the system is cold so the pressure used is cold fill which shows up on the tri gauge altimeter , pressure and temperature

To prove the 27.72 we times that by .433 which bring us back to the 12 PSI

As the water is heated it expands and this is why we use the expansion tank

All in the math

 

[Wrenched]

In my area the code simply asks for "protection against thermal expansion" in situations where it could be a problem(i.e pressure could exceed 80 psi or about 5.5 bar). There are a few ways to do this, in practice it usually means a thermal expansion tank or a combination ball and relief valve set to discharge at 80 psi. The ball and relief valves have become more popular because they are cheaper and easier to install, and when used as trap primer and hot water tank shut off, get three birds with one stone. They tend to fail more often, and are more work to replace. As a service plumber I find the expansion tanks much more reliable, as long as they have been sized and set properly. If thermal expansion isn't dealt with, usually the excess pressure causes a water closet fill valve to discharge, though it can also push through other fixtures, push back into the municipal system(almost all our prv have integral bypasses), or cause a system leak.

When you say "geyser" (it isn't a term we use here) are you referring to a tankless/on-demand system for potable water or to any system that heats hot water? The most common set up here is a nat. gas(CH4) forced-air furnace for space heating paired with a gas hot water tank. Gas-fired water boilers with base board heating or radiant in-floor heating are also fairly common, sometimes also used with an indirect tank for domestic hot water. Electric tanks are seen in places without gas service, or in hard to vent locations. Tankless/on-demand systems are much less common; the economics just aren't that great. Point-of-use heating is rare.
Our boilers have separate backflows, prvs, expansion tanks, and relief valves(emergency only) for closed systems.

Our PRVs are usually installed at the water entry point, but that is often an area without a floor drain/drainage.

What would be an example of the PRVs you use?

 

[PlumbSolve]

In my area the code simply asks for "protection against thermal expansion" in situations where it could be a problem(i.e pressure could exceed 80 psi or about 5.5 bar). There are a few ways to do this, in practice it usually means a thermal expansion tank or a combination ball and relief valve set to discharge at 80 psi. The ball and relief valves have become more popular because they are cheaper and easier to install, and when used as trap primer and hot water tank shut off, get three birds with one stone. They tend to fail more often, and are more work to replace. As a service plumber I find the expansion tanks much more reliable, as long as they have been sized and set properly. If thermal expansion isn't dealt with, usually the excess pressure causes a water closet fill valve to discharge, though it can also push through other fixtures, push back into the municipal system(almost all our prv have integral bypasses), or cause a system leak.

When you say "geyser" (it isn't a term we use here) are you referring to a tankless/on-demand system for potable water or to any system that heats hot water? The most common set up here is a nat. gas(CH4) forced-air furnace for space heating paired with a gas hot water tank. Gas-fired water boilers with base board heating or radiant in-floor heating are also fairly common, sometimes also used with an indirect tank for domestic hot water. Electric tanks are seen in places without gas service, or in hard to vent locations. Tankless/on-demand systems are much less common; the economics just aren't that great. Point-of-use heating is rare.
Our boilers have separate backflows, prvs, expansion tanks, and relief valves(emergency only) for closed systems.

Our PRVs are usually installed at the water entry point, but that is often an area without a floor drain/drainage.

What would be an example of the PRVs you use?

A geyser is what I think you term a hot water electric heater. We don't have piped gas in S Africa and so gas geysers are non existent We do get gas geysers but they are on demand units.
I have never seen a expansion tank on a geyser in S Africa. It is a criminal offence to install a geyser incorrectly. The reason being the energy stalled in superheated steam and it does kill. Our systems are simple. We have an inline PRV with built in pressure relief valve. They are normally rated 100kpa to 600kpa ,600 being the most popular. This PRV is installed before it enters the house. This balances the house so every fixture ,hot and cold will deliver the same pressure and this resolves balancing issues. The PRV needs to be over a drain as it will drip about 1,5 % of the volume of water it heats. When the water is hot it stops dripping. If the power is off it will also stop dripping.
Here is how our geysers look . The PRV is no 12.I wonder how two countries can have such different systems. I believe my country ,s system is easier and cheaper but the thing that stands out is that yours(if I understand correctly) wastes no water).We live in a water scarce country so all the geysers dripping would add up. What do you think?http://www.housecheck.co.za/hot-water-geysers/

 

[Reach4]

A geyser is what I think you term a hot water electric heater.

Do you often replace anodes?

 

[PlumbSolve]

Do you often replace anodes?

That geyser has some serious pressure. No we never change anodes. The geysers come with a 5 year manufacturers warrantee. 99% of all geysers I change are paid for by insurance so their is no incentive for the homeowner to do maintenance. Most geysers are 1.6mm thick and discounting water quality they last just over five years.