How to Select the Right Size Wates Pressure Vessel Before Installation

1. Introduction

• Why sizing a pressure vessel is critical before installation
• Undersized vessels cause rapid pump cycling, higher energy use, and early pump failure
• Oversized vessels increase cost and floor space without added benefit
• Wates vessels are available in multiple capacities (from 24 L to 5000+ L), so correct selection is essential

2. Role of a Pressure Vessel in a Domestic Water System

• Stores pressurized water to supply fixtures when pump is off
• Maintains stable pressure in the pipeline
• Reduces the number of pump starts per hour (standard design: 10–20 starts/hour max)
• Acts as a buffer tank to prevent water hammer and system shock

3. Key Factors to Consider Before Sizing a Wates Pressure Vessel
3.1 Pump Type

• Fixed-speed pump vs. VFD-controlled pump
• Fixed-speed pumps require larger vessel volume to control cycling
• VFD pumps may use smaller vessels but still need buffer volume for standby pressure retention

3.2 System Flow Demand

• Domestic villas: 30–60 LPM typical
• Small buildings: 80–150 LPM
• Larger systems or multi-pump sets: 200+ LPM

3.3 Required Number of Pump Starts per Hour

• Industry standard: 10–20 starts per hour to prevent motor damage
• More drawdown volume = fewer pump starts

3.4 Cut-In and Cut-Out Pressure

• Pressure settings determine usable drawdown volume
• Example: Cut-in 2.5 bar / Cut-out 4.0 bar

3.5 Available Space for Installation

• Vertical vessels require floor space
• Horizontal vessels can be mounted on top of the pump or frame

4. Basic Sizing Formula for Wates Pressure Vessels
The usable drawdown volume (water available per cycle) is calculated as:
Vd = Vt × (Pmax − Pmin) / (Pmax + 1)
Where:

• Vd = Drawdown volume (liters)
• Vt = Total vessel capacity (liters)
• Pmax = Maximum pressure (pump cut-out), in bar absolute
• Pmin = Minimum pressure (pump cut-in), in bar absolute

To find Vt:
Vt = Required Drawdown × (Pmax + 1) / (Pmax − Pmin)


5. Example Sizing Case (Domestic Villa Booster System)
System data:

• Pump cut-out pressure: 4.0 bar
• Pump cut-in pressure: 2.5 bar
• Desired pump starts per hour: 10
• Flow rate: 40 LPM
• Minimum water volume required: 40 L (4 minutes of standby between cycles)

Calculation:
Required Drawdown = 40 L
Total Vessel Size:
Vt = 40 × (4 + 1) / (4 − 2.5)
Vt = 40 × 5 / 1.5
Vt = 133 liters
Recommended Wates model: 150 L vertical vessel


6. Typical Wates Vessel Sizing Guide (Quick Reference)
Application
Flow Rate
Suggested Vessel Size

Small villa, 1–2 bathrooms
25–35 LPM
60 L to 80 L

Medium villa, 3–4 bathrooms
40–60 LPM
100 L to 150 L

Large villa or duplex
70–90 LPM
200 L

Small apartment building
100–150 LPM
300 L to 500 L

Multi-pump booster set
200+ LPM
500 L to 1000+ L


7. Common Sizing Mistakes Installers Make

• Selecting based on tank volume instead of usable drawdown
• Ignoring pump cut-in/cut-out settings
• Choosing 24 L or 50 L tanks for high-flow systems
• Not considering increased pump cycling from small tanks
• Assuming VFD pumps do not require pressure vessels

8. When to Use Multiple Pressure Vessels

• When system demand exceeds 500 L vessel capacity
• When installation footprint requires two smaller tanks instead of one large tank
• When redundancy is needed (e.g., hospitals, high-rise buildings)
• When connecting parallel booster pumps to a common header

9. UAE/GCC Installation Considerations

• High ambient temperatures require shaded tank location
• High-water hardness means bladder replacement frequency should be expected
• Stainless steel or lined tanks preferred for coastal areas (Dubai, Sharjah, Abu Dhabi)
• WRAS, PED, and CE certification required for potable water systems

Choosing the correct size Wates pressure vessel ensures:

• Longer pump lifespan
• Reduced energy consumption
• Stable and reliable water pressure
• Fewer maintenance issues and customer complaints

Sizing should always be based on drawdown volume, not total tank capacity. For more info contact Wates Pressure Vessel Supplier in UAE or call us at +971 4 2522966.

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