Zilmet Hydro-Pro 2 Litre Potable Expansion Vessel – 11A0000200 – ½" BSP
The Zilmet Hydro-Pro 2 is a 2-litre potable expansion vessel designed for domestic hot water systems, unvented cylinders, water heaters, pump sets, and anti-water-hammer applications.
The vessel uses a fixed Zilan DW diaphragm membrane — not a bladder — which isolates system water from the pre-charged air chamber. The membrane's seamless shape has no corners or creases where stagnant water or sediment can collect, actively inhibiting bacteriological growth and keeping the system hygienic. The carbon steel shell is finished internally with an exclusive epoxy powder coating and externally with an epoxy-polyester paint — both providing long-term corrosion resistance.
Technical Specifications
| Parameter | Value |
|---|---|
| MPN / Product code | 11A0000200 |
| Vessel volume | 2 litres |
| Connection | ½" BSP male (G½") |
| Max operating pressure | 10 Bar |
| Operating temperature range | -10°C to +99°C |
| Factory pre-charge pressure | 3.5 Bar |
| Shell material | Carbon steel — deep-drawn, MIG welded |
| Internal coating | Exclusive epoxy powder coating — corrosion resistant |
| External finish | Epoxy-polyester paint — rust resistant — blue/grey |
| Membrane type | Fixed Zilan DW diaphragm — food-grade, potable water approved |
| Connection fitting material | Carbon steel |
| Diameter (ØD) | 142mm |
| Height (H) | 196mm |
| Drawdown @ Pmax 10 Bar | 1.2 litres (heating) / 1.1 litres @ 0.8 L/min (pump duty) |
| Certifications | PED 2014/68/EU · WRAS · ACS · IAPMO · NSF |
| Manufacturer | Zilmet SpA, Limena, Padova, Italy |
Key Features
WRAS-approved potable water use
Holds international approvals for use with drinking water including WRAS (UK Water Regulations Advisory Scheme), ACS (France), IAPMO, and NSF. The Zilan DW fixed diaphragm membrane and internal epoxy coating are food-grade rated — suitable for unvented hot water cylinder installations and mains pressure systems.
Fixed Zilan DW diaphragm — no stagnation
The fixed diaphragm design has no creases, corners, or dead zones where water can stagnate. This seamless geometry actively inhibits bacteriological growth — important in any potable water application. Water and air are completely separated at all times; no waterlogging or pressure loss through air absorption.
Exclusive MIG welded construction
Zilmet's exclusive deep-drawn MIG welding process eliminates all interior sharp edges, rough spots, and weld profiles. This protects the diaphragm from damage over the life of the vessel and ensures the internal epoxy coating bonds uniformly across the entire shell — preventing localised corrosion.
Factory pre-charged and tested
Every Hydro-Pro 2 leaves the Zilmet factory pre-charged to 3.5 Bar and individually pressure-tested. The pre-charge valve is fitted with a protective cap. Pre-charge can be adjusted on site with a standard Schrader valve pump if the system static pressure requires a different setting.
Compact — 142mm diameter × 196mm height
At 142mm diameter and 196mm tall, the Hydro-Pro 2 fits easily in the airing cupboard next to an unvented cylinder or in a tight boiler cupboard. The ½" BSP male connection is standard across virtually all unvented cylinder expansion vessel connections and cold water expansion fittings.
Anti-water-hammer protection
In addition to thermal expansion duty, the Hydro-Pro 2 absorbs the pressure spikes caused by rapid valve closure and pump stop/start cycles — protecting downstream components, fittings, and appliances from shock damage. Suitable for installation on pump sets, boosters, and solenoid-valve-controlled circuits.
Applications & Sizing Guidance
The Hydro-Pro 2 is sized for small domestic applications where a compact vessel is required. Typical uses include thermal expansion relief on unvented hot water cylinders up to approximately 150 litres (at typical UK mains pressures), cold water expansion on combination boiler systems, and anti-water-hammer damping on pump sets and motorised valve circuits.
The correct vessel size for a given installation depends on the system volume, maximum working pressure, minimum static pressure, and temperature range. The pre-charge pressure should be set equal to the cold static fill pressure of the system. Zilmet publish a full drawdown and sizing calculator at their website. Vessel sizing must be verified by a competent installer or engineer.
Installation Notes
The Hydro-Pro 2 can be installed in any orientation — vertically (connection up or down) or horizontally — although vertical connection-up is preferred as it keeps the diaphragm correctly positioned over time. Install as close as possible to the appliance it is serving, with a suitable isolation valve and check valve upstream to prevent system pressure from affecting the pre-charge. For unvented cylinder duty, the vessel must comply with the G3 Building Regulation requirements for the installation; the vessel pressure rating must meet or exceed the maximum system pressure.
Frequently Asked Questions
Is the Hydro-Pro 2 suitable for an unvented hot water cylinder?
Yes — the Hydro-Pro 2 is WRAS approved for potable water use and rated to 10 Bar and 99°C, covering the operating conditions of domestic unvented cylinders. Confirm that the vessel capacity is correctly sized for the cylinder volume and system pressure range; for cylinders over approximately 150 litres a larger vessel will normally be required.
What is the factory pre-charge and can I adjust it?
The vessel leaves the factory pre-charged to 3.5 Bar. This is suitable for systems with a cold fill pressure up to 3.5 Bar. If your system cold fill pressure differs, adjust the pre-charge using a standard Schrader valve pump with the vessel isolated from the system and fully depressurised on the water side. Always set pre-charge equal to the cold static fill pressure before reconnecting.
What is the difference between a diaphragm vessel and a bladder vessel?
In a diaphragm vessel (like the Hydro-Pro), the membrane is fixed to the inside of the shell and divides the vessel into two chambers — water one side, air the other. In a bladder vessel the membrane is a free-floating bag. The Hydro-Pro's fixed diaphragm design means the membrane never creases or bunches, giving a longer service life and the seamless anti-stagnation geometry that makes it suitable for potable water duty.
How do I know when the expansion vessel needs replacing?
Common signs of a failed expansion vessel include the pressure relief valve on the cylinder discharging regularly, rapid pressure fluctuations when hot water is drawn, or the vessel feeling completely hard with no give when tapped. Check the pre-charge pressure annually — if the vessel holds no pre-charge even after re-pressurising, the diaphragm has failed and the vessel should be replaced.
Can the Hydro-Pro 2 also be used for anti-water-hammer duty on a pump set?
Yes — the Hydro-Pro range is explicitly rated and sized for anti-water-hammer applications on electric pump sets. The pre-charged air chamber absorbs the pressure spike created by rapid valve closure or pump stop. At Pmax 10 Bar, the Hydro-Pro 2 provides a drawdown of 1.1 litres at up to 0.8 L/min pump flow rate — sufficient for small domestic booster and pump applications.
Zilmet Hydro-Pro 5 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 8 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 12 Litre Potable Expansion Vessel | ½" BSP Check Valve | Expansion Vessel Bracket | Pressure Reducing Valve 15mm | 6 Bar Pressure Relief Valve 15mm
Original: $41.84
-65%$41.84
$14.64Zilmet Hydro-Pro 2 Litre Potable Expansion Vessel – 11A0000200 – ½" BSP
The Zilmet Hydro-Pro 2 is a 2-litre potable expansion vessel designed for domestic hot water systems, unvented cylinders, water heaters, pump sets, and anti-water-hammer applications.
The vessel uses a fixed Zilan DW diaphragm membrane — not a bladder — which isolates system water from the pre-charged air chamber. The membrane's seamless shape has no corners or creases where stagnant water or sediment can collect, actively inhibiting bacteriological growth and keeping the system hygienic. The carbon steel shell is finished internally with an exclusive epoxy powder coating and externally with an epoxy-polyester paint — both providing long-term corrosion resistance.
Technical Specifications
| Parameter | Value |
|---|---|
| MPN / Product code | 11A0000200 |
| Vessel volume | 2 litres |
| Connection | ½" BSP male (G½") |
| Max operating pressure | 10 Bar |
| Operating temperature range | -10°C to +99°C |
| Factory pre-charge pressure | 3.5 Bar |
| Shell material | Carbon steel — deep-drawn, MIG welded |
| Internal coating | Exclusive epoxy powder coating — corrosion resistant |
| External finish | Epoxy-polyester paint — rust resistant — blue/grey |
| Membrane type | Fixed Zilan DW diaphragm — food-grade, potable water approved |
| Connection fitting material | Carbon steel |
| Diameter (ØD) | 142mm |
| Height (H) | 196mm |
| Drawdown @ Pmax 10 Bar | 1.2 litres (heating) / 1.1 litres @ 0.8 L/min (pump duty) |
| Certifications | PED 2014/68/EU · WRAS · ACS · IAPMO · NSF |
| Manufacturer | Zilmet SpA, Limena, Padova, Italy |
Key Features
WRAS-approved potable water use
Holds international approvals for use with drinking water including WRAS (UK Water Regulations Advisory Scheme), ACS (France), IAPMO, and NSF. The Zilan DW fixed diaphragm membrane and internal epoxy coating are food-grade rated — suitable for unvented hot water cylinder installations and mains pressure systems.
Fixed Zilan DW diaphragm — no stagnation
The fixed diaphragm design has no creases, corners, or dead zones where water can stagnate. This seamless geometry actively inhibits bacteriological growth — important in any potable water application. Water and air are completely separated at all times; no waterlogging or pressure loss through air absorption.
Exclusive MIG welded construction
Zilmet's exclusive deep-drawn MIG welding process eliminates all interior sharp edges, rough spots, and weld profiles. This protects the diaphragm from damage over the life of the vessel and ensures the internal epoxy coating bonds uniformly across the entire shell — preventing localised corrosion.
Factory pre-charged and tested
Every Hydro-Pro 2 leaves the Zilmet factory pre-charged to 3.5 Bar and individually pressure-tested. The pre-charge valve is fitted with a protective cap. Pre-charge can be adjusted on site with a standard Schrader valve pump if the system static pressure requires a different setting.
Compact — 142mm diameter × 196mm height
At 142mm diameter and 196mm tall, the Hydro-Pro 2 fits easily in the airing cupboard next to an unvented cylinder or in a tight boiler cupboard. The ½" BSP male connection is standard across virtually all unvented cylinder expansion vessel connections and cold water expansion fittings.
Anti-water-hammer protection
In addition to thermal expansion duty, the Hydro-Pro 2 absorbs the pressure spikes caused by rapid valve closure and pump stop/start cycles — protecting downstream components, fittings, and appliances from shock damage. Suitable for installation on pump sets, boosters, and solenoid-valve-controlled circuits.
Applications & Sizing Guidance
The Hydro-Pro 2 is sized for small domestic applications where a compact vessel is required. Typical uses include thermal expansion relief on unvented hot water cylinders up to approximately 150 litres (at typical UK mains pressures), cold water expansion on combination boiler systems, and anti-water-hammer damping on pump sets and motorised valve circuits.
The correct vessel size for a given installation depends on the system volume, maximum working pressure, minimum static pressure, and temperature range. The pre-charge pressure should be set equal to the cold static fill pressure of the system. Zilmet publish a full drawdown and sizing calculator at their website. Vessel sizing must be verified by a competent installer or engineer.
Installation Notes
The Hydro-Pro 2 can be installed in any orientation — vertically (connection up or down) or horizontally — although vertical connection-up is preferred as it keeps the diaphragm correctly positioned over time. Install as close as possible to the appliance it is serving, with a suitable isolation valve and check valve upstream to prevent system pressure from affecting the pre-charge. For unvented cylinder duty, the vessel must comply with the G3 Building Regulation requirements for the installation; the vessel pressure rating must meet or exceed the maximum system pressure.
Frequently Asked Questions
Is the Hydro-Pro 2 suitable for an unvented hot water cylinder?
Yes — the Hydro-Pro 2 is WRAS approved for potable water use and rated to 10 Bar and 99°C, covering the operating conditions of domestic unvented cylinders. Confirm that the vessel capacity is correctly sized for the cylinder volume and system pressure range; for cylinders over approximately 150 litres a larger vessel will normally be required.
What is the factory pre-charge and can I adjust it?
The vessel leaves the factory pre-charged to 3.5 Bar. This is suitable for systems with a cold fill pressure up to 3.5 Bar. If your system cold fill pressure differs, adjust the pre-charge using a standard Schrader valve pump with the vessel isolated from the system and fully depressurised on the water side. Always set pre-charge equal to the cold static fill pressure before reconnecting.
What is the difference between a diaphragm vessel and a bladder vessel?
In a diaphragm vessel (like the Hydro-Pro), the membrane is fixed to the inside of the shell and divides the vessel into two chambers — water one side, air the other. In a bladder vessel the membrane is a free-floating bag. The Hydro-Pro's fixed diaphragm design means the membrane never creases or bunches, giving a longer service life and the seamless anti-stagnation geometry that makes it suitable for potable water duty.
How do I know when the expansion vessel needs replacing?
Common signs of a failed expansion vessel include the pressure relief valve on the cylinder discharging regularly, rapid pressure fluctuations when hot water is drawn, or the vessel feeling completely hard with no give when tapped. Check the pre-charge pressure annually — if the vessel holds no pre-charge even after re-pressurising, the diaphragm has failed and the vessel should be replaced.
Can the Hydro-Pro 2 also be used for anti-water-hammer duty on a pump set?
Yes — the Hydro-Pro range is explicitly rated and sized for anti-water-hammer applications on electric pump sets. The pre-charged air chamber absorbs the pressure spike created by rapid valve closure or pump stop. At Pmax 10 Bar, the Hydro-Pro 2 provides a drawdown of 1.1 litres at up to 0.8 L/min pump flow rate — sufficient for small domestic booster and pump applications.
Zilmet Hydro-Pro 5 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 8 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 12 Litre Potable Expansion Vessel | ½" BSP Check Valve | Expansion Vessel Bracket | Pressure Reducing Valve 15mm | 6 Bar Pressure Relief Valve 15mm
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
The Zilmet Hydro-Pro 2 is a 2-litre potable expansion vessel designed for domestic hot water systems, unvented cylinders, water heaters, pump sets, and anti-water-hammer applications.
The vessel uses a fixed Zilan DW diaphragm membrane — not a bladder — which isolates system water from the pre-charged air chamber. The membrane's seamless shape has no corners or creases where stagnant water or sediment can collect, actively inhibiting bacteriological growth and keeping the system hygienic. The carbon steel shell is finished internally with an exclusive epoxy powder coating and externally with an epoxy-polyester paint — both providing long-term corrosion resistance.
Technical Specifications
| Parameter | Value |
|---|---|
| MPN / Product code | 11A0000200 |
| Vessel volume | 2 litres |
| Connection | ½" BSP male (G½") |
| Max operating pressure | 10 Bar |
| Operating temperature range | -10°C to +99°C |
| Factory pre-charge pressure | 3.5 Bar |
| Shell material | Carbon steel — deep-drawn, MIG welded |
| Internal coating | Exclusive epoxy powder coating — corrosion resistant |
| External finish | Epoxy-polyester paint — rust resistant — blue/grey |
| Membrane type | Fixed Zilan DW diaphragm — food-grade, potable water approved |
| Connection fitting material | Carbon steel |
| Diameter (ØD) | 142mm |
| Height (H) | 196mm |
| Drawdown @ Pmax 10 Bar | 1.2 litres (heating) / 1.1 litres @ 0.8 L/min (pump duty) |
| Certifications | PED 2014/68/EU · WRAS · ACS · IAPMO · NSF |
| Manufacturer | Zilmet SpA, Limena, Padova, Italy |
Key Features
WRAS-approved potable water use
Holds international approvals for use with drinking water including WRAS (UK Water Regulations Advisory Scheme), ACS (France), IAPMO, and NSF. The Zilan DW fixed diaphragm membrane and internal epoxy coating are food-grade rated — suitable for unvented hot water cylinder installations and mains pressure systems.
Fixed Zilan DW diaphragm — no stagnation
The fixed diaphragm design has no creases, corners, or dead zones where water can stagnate. This seamless geometry actively inhibits bacteriological growth — important in any potable water application. Water and air are completely separated at all times; no waterlogging or pressure loss through air absorption.
Exclusive MIG welded construction
Zilmet's exclusive deep-drawn MIG welding process eliminates all interior sharp edges, rough spots, and weld profiles. This protects the diaphragm from damage over the life of the vessel and ensures the internal epoxy coating bonds uniformly across the entire shell — preventing localised corrosion.
Factory pre-charged and tested
Every Hydro-Pro 2 leaves the Zilmet factory pre-charged to 3.5 Bar and individually pressure-tested. The pre-charge valve is fitted with a protective cap. Pre-charge can be adjusted on site with a standard Schrader valve pump if the system static pressure requires a different setting.
Compact — 142mm diameter × 196mm height
At 142mm diameter and 196mm tall, the Hydro-Pro 2 fits easily in the airing cupboard next to an unvented cylinder or in a tight boiler cupboard. The ½" BSP male connection is standard across virtually all unvented cylinder expansion vessel connections and cold water expansion fittings.
Anti-water-hammer protection
In addition to thermal expansion duty, the Hydro-Pro 2 absorbs the pressure spikes caused by rapid valve closure and pump stop/start cycles — protecting downstream components, fittings, and appliances from shock damage. Suitable for installation on pump sets, boosters, and solenoid-valve-controlled circuits.
Applications & Sizing Guidance
The Hydro-Pro 2 is sized for small domestic applications where a compact vessel is required. Typical uses include thermal expansion relief on unvented hot water cylinders up to approximately 150 litres (at typical UK mains pressures), cold water expansion on combination boiler systems, and anti-water-hammer damping on pump sets and motorised valve circuits.
The correct vessel size for a given installation depends on the system volume, maximum working pressure, minimum static pressure, and temperature range. The pre-charge pressure should be set equal to the cold static fill pressure of the system. Zilmet publish a full drawdown and sizing calculator at their website. Vessel sizing must be verified by a competent installer or engineer.
Installation Notes
The Hydro-Pro 2 can be installed in any orientation — vertically (connection up or down) or horizontally — although vertical connection-up is preferred as it keeps the diaphragm correctly positioned over time. Install as close as possible to the appliance it is serving, with a suitable isolation valve and check valve upstream to prevent system pressure from affecting the pre-charge. For unvented cylinder duty, the vessel must comply with the G3 Building Regulation requirements for the installation; the vessel pressure rating must meet or exceed the maximum system pressure.
Frequently Asked Questions
Is the Hydro-Pro 2 suitable for an unvented hot water cylinder?
Yes — the Hydro-Pro 2 is WRAS approved for potable water use and rated to 10 Bar and 99°C, covering the operating conditions of domestic unvented cylinders. Confirm that the vessel capacity is correctly sized for the cylinder volume and system pressure range; for cylinders over approximately 150 litres a larger vessel will normally be required.
What is the factory pre-charge and can I adjust it?
The vessel leaves the factory pre-charged to 3.5 Bar. This is suitable for systems with a cold fill pressure up to 3.5 Bar. If your system cold fill pressure differs, adjust the pre-charge using a standard Schrader valve pump with the vessel isolated from the system and fully depressurised on the water side. Always set pre-charge equal to the cold static fill pressure before reconnecting.
What is the difference between a diaphragm vessel and a bladder vessel?
In a diaphragm vessel (like the Hydro-Pro), the membrane is fixed to the inside of the shell and divides the vessel into two chambers — water one side, air the other. In a bladder vessel the membrane is a free-floating bag. The Hydro-Pro's fixed diaphragm design means the membrane never creases or bunches, giving a longer service life and the seamless anti-stagnation geometry that makes it suitable for potable water duty.
How do I know when the expansion vessel needs replacing?
Common signs of a failed expansion vessel include the pressure relief valve on the cylinder discharging regularly, rapid pressure fluctuations when hot water is drawn, or the vessel feeling completely hard with no give when tapped. Check the pre-charge pressure annually — if the vessel holds no pre-charge even after re-pressurising, the diaphragm has failed and the vessel should be replaced.
Can the Hydro-Pro 2 also be used for anti-water-hammer duty on a pump set?
Yes — the Hydro-Pro range is explicitly rated and sized for anti-water-hammer applications on electric pump sets. The pre-charged air chamber absorbs the pressure spike created by rapid valve closure or pump stop. At Pmax 10 Bar, the Hydro-Pro 2 provides a drawdown of 1.1 litres at up to 0.8 L/min pump flow rate — sufficient for small domestic booster and pump applications.
Zilmet Hydro-Pro 5 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 8 Litre Potable Expansion Vessel | Zilmet Hydro-Pro 12 Litre Potable Expansion Vessel | ½" BSP Check Valve | Expansion Vessel Bracket | Pressure Reducing Valve 15mm | 6 Bar Pressure Relief Valve 15mm
