A better solution for water reticulation in high rise buildings

Water supply in high rise buildings is traditionally achieved as follows:

Gravity?Feed?from?a?tank?at?the?top?of?the?building

This?entails?pumping?water?up?from?ground?level?of?a?municipal?supply,?which?can?be?at?anything?between?3?to?6bar?pressure.?Pumps?have?to?be?used?to?get the?water?to?the?top?of?the?building?and?into?storage?tanks.?From?the?storage?tanks?the?water?will?flow?down?the?building?in?pipes,?with?off-takes?at?each floor.?Due?to?the?increase?in?pressure?as?the?water?flows?down?(1bar?for?every?10m),?Pressure reducing valves (PRVs) have to be installed at various levels, dictated by the incoming pressure at that level, the chosen?pipe?rating?and?the?accepted?“comfortable”?pressure?for?taps,?showers?and?any?other?water consuming?appliances.

Notes:

• It is good practice to install PRVs in paralled with isolating valves to ensure continuous supply in case of breakages/maintenance
• In some cases up to 4 PRVs have to act in series
• It is good practice to install a Relief valve after each PRV station.

Which?Pressure?Reducing?valves?to?select?

Direct Acting PRVs?(DAPRVs)

These?valves?are?actuated?by?a?Spring?and?Diaphragm?and?are?adjustable?–?(see?attached?picture).?Although?a?simpleform?of?Pressure Reducing valve with advantages of quick reaction time and simplicity, their major shortcoming is a limit to their capacity. Installing?a?full?size?PRV?in?a?Pipeline?(ie?100mm?valve?in?a?100mm?Pipeline),?a?situation?can?often?beexperienced?where?the?valve?is?not?able?to?cope?with?the?high?demand,?so?this?criteria?has?to?be?carefully?checked?before installation.

Pilot?Operated?PRVs?(POPRVs)

These?valves?have?been?the?traditional?PRV?of?choice?in?High?Rise Buildings as they have no problem with standard demand?patterns?and?are?oftensized?one?size?smaller?than?Line?size. There?are?however?three?issues?which?the?Design?Engineer?has?to consider carefully with their use:

1. PRVs?acting?in?series.?This?is?often?a?requirement?in?High?Rise?Buildings?as?indicated?in?the?reticulation?schematic. These?valves?have?to?befinely?“tuned”?when?they?are acting in series in order to eliminate unstable operation caused by “hunting” between the two valves. Even then when?someone?disturbs?this?setting,?the?results?could?be catastrophic and result in burst pipes.
2. Low?Flow?capability.?In?High?Rise?Buildings?(or?any?domestic?reticulation?for?that?matter),?POPRV’s?will?become?unstable when they have to operate at very low flows. This?instability?can?also?result?in?burst?pipes.?Although?the?problem?can?be?overcome?by?installing?a?small?DAPRV in?parallel,?and?which?will?automatically?take?over?at?low demand?times,?it?makes?the?system?more?complex?and?vulnerable to tampering.
3. Reaction Time delay.?Because POPRV’s take time to react?to?demand?changes,?it?is?often?advisable?to?install?a?relief valve?on?the?downstreamside?of?the?valves?to?cater?for sudden demand reductions.

Ratio?Reducing?Valves?(RRV’s)

A?Ratio?Reducing?Valve?reduces?pressure?in?a?ratio?between inlet?and?outlet?pressure?–?so?if?you?have?a?2:1?RRV,?it?would?reduce?an?inlet?pressure?of10bar?to?5bar.?Similarly?a?RRV?with?3:1?ratio?would?reduce?a?pressure?of?12bar?to?4bar?etc.?A?RRV?is?non-adjustable?and?has?no?external?Pilots?oraccessories which can be tampered with or broken.?

Advantages of the Ratio?Reducing Valve:

• Extremely?simple. The?only?working?part?is?a?Piston
• Very?fast?reaction?times. This makes?the?RRV?suitable?to?act?in?series?without?instability.?It?is?also?not?totally?necessary?to?install?a?Relief?valvedownstream,?although?a?conservative?option would be to install one anyway and with the knowledge that it will seldom operate.
• Capable?of?handling?low?flow?without?becoming?unstable.?So?one?valve?would?normally?handle?the?whole?range?of flows required without a Bypass valve required.

The?Ratio?Reducing?valve?has?been?used?successfully?in?buildings?in?Australia?where?one?of?the?first?Ratio?Reducing?valves has been developed.

In?South?Africa?this?product?has?been?used?in?the?Mining?Industry?with?great?success?and?where?Water?Reticulation?is?similar?to?that?in?High?Risebuildings.?Because?of?the?higher pressures?used?in?the?Mining?Industry?than?in?most?High?Rise?Buildings,?some?companies?developed?a?range?ofRatio?Reducing valves for higher pressures.

Ultra?have?a?range?of?RRV’s?up?to?300mm?size?and?100bar?pressure?rating

Flow?Control?for?various?appliances

Now?that?we?have?described?a?better?solution?for?getting?the?pressures to suitable figures on each floor level, consideration?should be given to distributing the water at ideal flow rates (and?pressures)?for?the?various?appliances?such?as showers, taps and water heaters.

The?benefit?of?regulating?the?flows?and?pressures?to?the?ideal?levels?is?better?distribution?of?water?to?ensure?that?one?area?or?appliance?does?not?takemore?than?required?and?potentially starve?other?areas,?and?more?importantly?to?conserve?water?which?has?become?a?very?important?issue?in?todayswater- starved countries such as South Africa.

Maric?Flow?Control?Valves?,manufactured?in?Australia,?have?been?available?in?SA?for?many?years. These valves are?used?to evenly distribute water throughout buildings such as High?Rise?Buildings,?hospitals?and?hotels?etc,?where?multiple?users?and?off-takes?make?proper?control?difficult.?These relatively inexpensive?and?simple?devices?offer?an?excellent?solution?to?proper?flow?and?pressure?distribution?and?will?result?in?very fast return on investment for these buildings.

A?video?explaining?the?operation?of?the?Maric?can?be viewed?on?our?website?www.ultravalves.co.za?under?Control?Valves/Flow?Control Valves.