2 hours ago, Muhendis said:

Take care with Crossy's bypass.

I would imagine he forgot the stop valve unless, of course, that strange looking check/non-return valve includes one.

I always thought the NRV symbol was similar to an electronic diode. You live and learn I guess.

Additional non return not always required. Extra points for guessing its purpose.

Extra points for guessing its purpose.

Yep! That's easy.

If the cock is left on the chickens may try to return to the meter.

Did I win?

3 hours ago, Muhendis said:

Extra points for guessing its purpose.

Yep! That's easy.

If the cock is left on the chickens may try to return to the meter.

Did I win?

Correct, without additional NRV the chickens would indeed return to the meter never to return. ⇦🐓🐓🐓🐓🐓🐓

However, there's a less important reason.

Automatic house pumps leaking from seals or gaskets that have been lifted or blown out.

Reply from a manufacturer. Our pumps are not designed to compete with local water supply pressure which often contains pressure spikes well above the pumps rating.

1 hour ago, Fruit Trader said:

Reply from a manufacturer. Our pumps are not designed to compete with local water supply pressure which often contains pressure spikes well above the pumps rating.

I'll tell that one to our local water department.

It's been ages since they had a good laugh.

Under pressure, yes.

Over pressure, never.

This thing about house supply pumps.

As long as the pump is supplied from the local storage tank only, then there will be no overpressure problem.

1 hour ago, Muhendis said:

As long as the pump is supplied from the local storage tank only, then there will be no overpressure problem.

Look at the diagram then think again.

At low consumption periods the pressure has reached 5+ bar here. The worst spikes from city water can come after a repair during repressurising of the system. Not everyone lives on a trickle feed.

2 hours ago, Fruit Trader said:

Look at the diagram then think again.

There is a local tank in the diagram into which utility water at random pressure is supplied via a float valve/ball cock.

The house pump receives water from this storage tank only. How on earth do you get your 5+ Bar pressure from that?

Please note:

The only time utility water will be directly connected to the house plumbing is when the bypass valve is opened which would only happen

in an emergency and even then it would not be present at the input to the house pump.

3 hours ago, Fruit Trader said:

Look at the diagram then think again.

At low consumption periods the pressure has reached 5+ bar here. The worst spikes from city water can come after a repair during repressurising of the system. Not everyone lives on a trickle feed.

Then try to get a pop off valve (pressure relief valve) and install on your manifold, so if the city water spikes you have a valve that release the exceeded pressure, and you do not damage anything.

3 hours ago, Hummin said:

Then try to get a pop off valve (pressure relief valve) and install on your manifold, so if the city water spikes you have a valve that release the exceeded pressure, and you do not damage anything.

Yes that's the best solution although a pressure limiting valve would be the better choice to a relief valve which dumps excess pressure to waste.

3 hours ago, Muhendis said:

There is a local tank in the diagram into which utility water at random pressure is supplied via a float valve/ball cock.

The house pump receives water from this storage tank only. How on earth do you get your 5+ Bar pressure from that?

Please note:

The only time utility water will be directly connected to the house plumbing is when the bypass valve is opened which would only happen

in an emergency and even then it would not be present at the input to the house pump.

Almost all installations have no emergency bypass valve, the backup is automatic. Look at the original diagram by @Crossy .

The common setup is quite simply a pressure wins situation and the pump gets the full pressure from street supply.

14 hours ago, Fruit Trader said:

Look at the diagram then think again.

At low consumption periods the pressure has reached 5+ bar here. The worst spikes from city water can come after a repair during repressurising of the system. Not everyone lives on a trickle feed.

The pump should never be connected directly to the mains water supply, it should always get its gravity feed supply from a water tank, this completely eliminates any overpressure or pressure spike issues.

3 minutes ago, Wotsup said:

The pump should never be connected directly to the mains water supply, it should always get its gravity feed supply from a water tank, this completely eliminates any overpressure or pressure spike issues.

Plus it is illegal to do so.

8 hours ago, Fruit Trader said:

Almost all installations have no emergency bypass valve, the backup is automatic. Look at the original diagram by @Crossy .

The common setup is quite simply a pressure wins situation and the pump gets the full pressure from street supply.

That statement is so, so wrong! all surface water pressure pumps are designed to be gravity fed from a storage tank, the pump never see's the mains water pressure. It is also not allowed by the PWA and MWA to connect a pressure pump directly in series with the mains supply.

23 hours ago, Muhendis said:

Take care with Crossy's bypass.

I would imagine he forgot the stop valve unless, of course, that strange looking check/non-return valve includes one.

I always thought the NRV symbol was similar to an electronic diode. You live and learn I guess.

Not necessary, the "stop valve is at the property boundary" as it is if you didn't have a tank and pump system.

7 minutes ago, Artisi said:

Plus it is illegal to do so.

It is not illegal to pump directly from municipal water supply.

It is generally bad practice.

2 minutes ago, Yellowtail said:

It is not illegal to pump directly from municipal water supply.

It is generally bad practice.

Not bad practice, not allowed.

5 minutes ago, Artisi said:

Not bad practice, not allowed.

So you've gone from illegal to not allowed....

14 minutes ago, Artisi said:

Not necessary, the "stop valve is at the property boundary" as it is if you didn't have a tank and pump system.

You seem to be saying it is OK to have the utility supply connected without a valve in the bypass of the storage tank and the house pump.

I would be less than happy about that.

At my place there's a stop valve (ball valve) directly after meter before entering property and I have another on my side before entering house. This is without a tank.

21 minutes ago, Yellowtail said:

So you've gone from illegal to not allowed....

Grow up.

illegal was a comment saying it is against the rules.

So, you seem to believe you can do what ever you want, is that right?

9 hours ago, Fruit Trader said:

Yes that's the best solution although a pressure limiting valve would be the better choice to a relief valve which dumps excess pressure to waste.

The relief valve can go on a line or the circulation line to the tank. And why a circulation line is good to have, if you want to treat your tank with chemicals for cleaning.

1 hour ago, Wotsup said:

That statement is so, so wrong! all surface water pressure pumps are designed to be gravity fed from a storage tank, the pump never see's the mains water pressure. It is also not allowed by the PWA and MWA to connect a pressure pump directly in series with the mains supply.

I suggest you bring yourself up to speed with the standard automatic backup system employed in Thailand. AI has also picked up on the method if you need a detailed explanation. @Crossy has provided a diagram that shows the standard setup.

For those who think this auto backup arrangement with back flow prevention is illegal, call your local supply authority and you might get a little surprise. This is not the same as booster pumps which can apply negative pressure to the mains water line and in some cases might not be allowed by supply authority..

Video that shows standard auto backup system. Note: The tank used in this video has its inlet and outlet conveniently located at the bottom of the tank. City (mains) water is on the pipe arriving behind the tank.

For those who cant grasp where the pressure spike might be a problem.

When we built our home the daytime mains pressure wasn't enough to fill the tank!

It's much better now but we still can't use the showers upstairs unless the pump is available.

If you are worried about spikes in mains pressure you can add a stop valve in series with the bypass (you should still use the NR valve too), it just means your bypass becomes manual.

2 hours ago, Artisi said:

Not bad practice, not allowed.

Not allowed by whom? Who checks?

On 4/22/2026 at 8:49 AM, Muhendis said:

Take care with Crossy's bypass.

I would imagine he forgot the stop valve unless, of course, that strange looking check/non-return valve includes one.

You live and learn I guess.

Agh ! First the AN grammar police. Now the AN P&ID police. 😄

On 4/22/2026 at 8:49 AM, Muhendis said:

I always thought the NRV symbol was similar to an electronic diode.

Nah. The electronic symbol has a stylized bold arrow inline.

The flow diagram symbol has a 45-deg stick man type arrow or sometimes a stick man arrow parallel to the flow but outside the valve symbol.

Most everyone with a roof-tank is pumping from the water main to fill the tank.

We have a five-floor shophouse in Bangkok. It has a roof-tank, and the water will not fill the tank without a pump. It is in a row of ten shophouses all with roof-tanks. They all pump from the water main to fill the tanks.

We added ground tanks, so we do not draw from the main. The main fills the ground tanks, we pump from the ground tanks to the roof-tank, and we pump the water down into the house.

7 hours ago, Fruit Trader said:

I suggest you bring yourself up to speed with the standard automatic backup system employed in Thailand. AI has also picked up on the method if you need a detailed explanation. @Crossy has provided a diagram that shows the standard setup.

For those who think this auto backup arrangement with back flow prevention is illegal, call your local supply authority and you might get a little surprise. This is not the same as booster pumps which can apply negative pressure to the mains water line and in some cases might not be allowed by supply authority..

Video that shows standard auto backup system. Note: The tank used in this video has its inlet and outlet conveniently located at the bottom of the tank. City (mains) water is on the pipe arriving behind the tank.

For those who cant grasp where the pressure spike might be a problem.

That set up is exactly as I stated, the pump is gravity fed from the water tank, your were implying that you connected the mains supply directly to your pump inlet with no water tank at all.

9 hours ago, Yellowtail said:

It is not illegal to pump directly from municipal water supply.

It is generally bad practice.

For it to be illegal it would have to be a statute law, which it is not, it is however not allowed by the PWA or the MWA because as you say it is bad practice.

3 hours ago, Wotsup said:

That set up is exactly as I stated, the pump is gravity fed from the water tank, your were implying that you connected the mains supply directly to your pump inlet with no water tank at all.

Interesting, now where did I imply that I connected the mains supply directly to my pump inlet without a tank. Even more interesting is we don't have city water anywhere near our house pump, we take water from the packing shed well tank. City water is on our land though, BIL and MIL use it directly into their houses and it's backup for our packaging process.

Any more little fictitious stories you would like to share.

19 hours ago, Yellowtail said:

It is not illegal to pump directly from municipal water supply.

It is generally bad practice.

9 hours ago, Wotsup said:

For it to be illegal it would have to be a statute law, which it is not, it is however not allowed by the PWA or the MWA because as you say it is bad practice.

Illegal means: against the law, rules or regulations, therefore pumping directly to the main water is "illegal" - and for a good reason, which you should check why if don't know.

5 hours ago, Artisi said:

Illegal means: against the law, rules or regulations, therefore pumping directly to the main water is "illegal" - and for a good reason, which you should check why if don't know.

Bottom line is the law can be applied if required.

Under Thai law both PWA and MWA have the authority to dictate how customers connect to their supply but like just about everything here it comes down to reality vs enforcement. Get found out as a source of contamination and the law would very quickly be applied.

We wash product using well water and have the city water as backup. The local authority has made one inspection in ten years to look at our well, how we use city water, how we dispose of waste water and to see if we are a contamination risk. I believe the frequency of these inspections vary between provinces.