Zilmet Ultra Pro Expansion Vessel with interchangeable membrane for Potable Water Horizontal 300ltr

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An Expansion Vessel is used to balance pressure in a sealed central heating system, as water cannot be compressed. Sometimes used by customers as an accumulator, an expansion vessel contains a bladder or diaphragm that is charged with air to a suitable pressure to help when demand for water is higher. This WRAS approved Horizontal expansion vessel is suitable for Potable water, comes with an interchangeable (replaceable) membrane for maintenance purposes and is fitted with a 1.5" size connection.
5 year guarantee
  • Potable Water Expansion Vessel for potable water, pumps and booster sets
  • Max. working pressure: 10 bar
  • Max. operating temperature: 70°C
  • Factory Pre-charge: 1.5 bar
  • Vessel Capacity: 300 Litre Horizontal
  • Connection: 1 1/2" MBSP
  • Flange: Galvanised Steel/Stainless Steel
  • Membrane: Replaceable membrane - either Butyl or EPDM
  • Shell: Carbon Steel
  • Colour: Blue
  • Diameter: 630mm
  • Height: 660mm
  • Length: 1140mm
Cold water accumulators buffer tank working on mains pressure precharge to increase your water flow

For example if you run your water tap at 4 am you will find that there is a greater amount of pressure coming from your mains outlet, this pressure will be stored in your Buffer tank and will allow you to use this over the following day. Also as its a tank you are able to increase the flow of water into your property. This giving you a greater volume of water and better pressure than you would have in the middle of the day. This can give the property the feeling of a massive pump being installed in to the home when its only the use of the stored pressure in the buffer tank. Now this pressure will only be as good as the pressure your property has at any one time and the volume will only be as good as the size of tank you choose and the outlet and size of pipework from the tank. This is a relatively easy system to install and give massive benefits to the home and does allow bigger shower heads and quicker filling of baths or if used in commercial use huge gains in the volume of water available. This tanks can also be linked together to give huge amounts of water volume. This really is a maxing fix for a home with a low water pressure due to large demand on volume

 With a greater demand for and the introduction of mains fed appliances, like for instance: electric showers, combination boilers, and unvented cylinders. The mains supply for both pressure (the force of water measured in bar or PSI) and flow rate, (the amount of water measured in litres or gallons) is so important, nowadays.

A poor mains supply coming in to the property will cause pressure and flow fluctuations, as well as ultimately poor performance leading to dissatisfaction and very troubled wash times for the whole house. We’re sure lots of you have had to perform a whole host of dance moves under an electric shower to just get covered in water, or when you run the bath and it takes so long that by the time it’s finished running the water is cold.

With high performance showers becoming ever more popular, much like this one ****** and popularity in multi bathroom properties, the demands of the mains water supply are so much higher. Often the performance needs of the mains supply to meet the demands of these showers or properties is overlooked.

As many of the water systems in the UK can be victorian; they are just not able to keep up with the demand needed for more water... But now with a water accumulator in the setup, it can be.

The legal supply requirement from water companies (undertakers) is 1 bar and 9 litres at the water companies stop tap (road stop cock), which is often located at the metre, but this position can vary. It is not common to have pressure and flow readings this low, but it is common place to find poor flow rates with average pressures of around (2-3) bar, leading to pressure fluctuations and ultimately poor performance and unhappy household.

Accumulator technology is one way of overcoming poor flow rates by storing cold mains water in a sealed vessel, increasing volume and stabilising pressures to combination boilers, unvented cylinders and much much more.

Accumulators are not a new concept and have been used in many applications worldwide such as applications on ships, aircraft, farms as well as commercial pump sets. Using accumulator technology to help boost mains supplies.

We always recommend that you check the incoming mains pressure before installing a cold water accumulator in to your property this is to make sure that you will get the best results from the increased water flow in daytime use. Some properties don't have enough water pressure to give a significant increase in flow but may still may be better than what is previously available. we want you to have the best results so always want you as the customer to know what the biggest pressure you will gain from this increase in mains water flow in the house by fitting this cold water accumulator. Also by knowing your water pressure we are able to advise you of the best cold water system to install into your property as there are many other available and we can recommend the best one to suite your home. (pressure will be the same as highest point of 24 hours period)

Once you have your readings the next criteria required is that of demand: number of outlets, people living at the property, typical daily usage and taps and bath/shower specification. The more bathroom/ensuites and hot and cold outlets the larger the demand and the bigger the accumulator required. For high demand more than one accumulator can be installed in series to meet requirements, making them an ideal solution for sports clubs, small hotels and care homes.

The accumulator design has no power supply, drainage requirements or running cost and the design has on average a 50% air to 50% water ratio and when being used the accumulators cannot replenish until the outlets being run are no longer in use and turned off. All these factors mean the cold water accumulator must be oversized. Another key factor is the lower the pressure the lower the volume that can be stored in the vessel. So you will need bigger cold water accumulator to compensate for lower pressure and even in some cases a pump can be fitted but we feel this defeats the object of a eco friendly system that will have a longer life cycle and keep working with less complications with non pump fitted.

Accumulators can be used to increase flow rates to mains fed appliances such as combination boilers and some hot water systems. You can also have a similar version of this in hot water by buying a unvented cylinder this will give you a cold water accumulator for hot water these are called unvented cylinders and also greatly increase your hot water flow and pressure when installed correctly

Cold water accumulators have been fitted in the UK for many years and lots of companies have offered this technology to increase flow rates on mains supplies and now with a bigger percentage of combi combination boilers being sold and installed in UK homes, the cold water accumulator is the perfect answer to overcome shared mains, and high demands from flats in the same building when used with combination boilers are installed. This has been a big challenge to overcome when building a property with more efficiency in mind as a combination boiler cannot always be installed as low mains pressure (flow rate). Also Combi boilers are a very cost effective product currently and do save some pounds with some brands to your pocket or development if able to be installed. How it works the cold water accumulator is installed on the main supply where it provides an increase in water volume that helps maintain the flow rate produced by the combination boiler and without interruptions from other outlets within the building at peak times or from cold outlets within the property. On new installations with high flow combination boilers the accumulator can offer increased flow rates, stable pressures and given the boiler specification, performances more impressive than those normally associated with standard combination boilers.

Because each application is different it is difficult to give a simple sizing chart that would cover all options, and we would recommend contacting Tradeplumbing Technical Team to discuss your individual requirements. Sizes and weights of each accumulator model can be viewed under technical specification in each of the products. We also do have access to a huge amount of manufacturers and will always gain are knowledge to make sure you have the best suited system for your property we still always recommend that you have a qualified plumber to make the final decisions as its very important to have a onsite opinion and advice to what is best for you. One main factor to consider is the weight of the accumulator and where to put this as some properties would need reinforcing if it was to be situated in a loft or airing cupboard.


Some questions that we get asked about cold water accumulators (buffer tank)


  1. Can accumulators be installed on 15mm or shared main supplies

    1. Answer. Yes. Carry out pressure and flow tests then oversize the accumulator to meet demand that you require this is a great use of a cold water accumulator to increase you flowrate to the property

  2. Can the accumulators be installed horizontally in a loft?

    1. Answer. Yes. You will need to choose the Horizontal version as vertical versions cannot be used horizontally and some brands can only be used vertically as it voids the warranty if used in this manner.

  3. Can the accumulators be installed outside, in a open garage or shed?

    1. Answer. Yes. ,the stainless steel range is ideal and designed with this in mind, remembering no power supply, or drainage is required so they can go almost anywhere, basements garages etc. The pipe size can also be run in plastic from the accumulator to the house in the correct size needed to keep a high flowrate of water to your property.

  4. Can I drink the cold water from an accumulator?

    1. Yes, ideally we recommend a separate drinking supply as requested in water regulations, but the accumulators have been tested and passed for use on potable water, and the butyl liner contains no harmful Pilates

  5. How efficient is the accumulator?

    1. Very is the simple answer, yes there is a carbon footprint in the production in shipping, but once installed the accumulator requires no power supply, consumes no energy and is silent in operation, there are also no on going maintenance costs

  6. Does the accumulator improve my pressure and by how much?

    1. No, Cold water accumulators are designed to increase flow rate and stabilize your pressures, although the effect of having the accumulator on the system for most people seems like as if the pressure has been increased. There is a standing pressure, which is the pressure when no outlets are being used and a working pressure the pressure when outlets are running. When the accumulator is linked into the system the increased flow rate helps to maintain the pressure close to the original standing pressure but with a better flow rate, for as long as water is stored in the accumulator. This is why you may need bigger cold water accumulators than you would have hot water tank.

  7. Do the accumulators make any noise when in operation?

    1. No, there are no working parts within the vessel and therefore no noise issues, water at a good pressure can caused noise through pipe work if not clipped or supported but no noise from the accumulator. And with no power supply or running cost or ongoing maintenance it is both a greener and more efficient option.

  8. I have a combination boiler and the incoming flow rate is poor, can an accumulator be used to increase the flow rate?

    1. Yes, many installations where an accumulator will be used in conjunction with a new or existing combination boiler. Carry out pressure and flow tests and then select the accumulator size required, normally a 200L or 300L models or above. The accumulator will increase the flow rate allowing the combi to run at its maximum given flow rate and not be interrupted by other cold outlets being run. For an impressive performance look one of the new breed of combi store boilers, that have 40,50 litres of unvented store, linked with an accumulator you get a huge amount of flow rate.

  9. I have seen other websites mentioning accumulators, why should I choose your products?

    1. We have over 30 years experience in the plumbing and heating industry, and in this time have developed and sourced the best products for our customers giving good value for money from top quality manufacturers.


expansion vessel for potable water, pumps and booster sets
capacity: from 24 - 3000 litres

ULTRA-PRO pressure tanks are the best choice for irrigation pumps, centrifugal pumps, submersible pumps and
for booster sets. The capacity of a bladder tank is larger than the capacity of common storage tanks: the same
performance can be obtained with a smaller volume, allowing minimum pump starts therefore saving energy.
The range of different sizes, availability of vertical and horizontal models, together the choice between galvanised
or stainless steel fl anges ensure that the ULTRA-PRO pressure tanks meet the requirements of the end user. Pressure
tanks from Zilmet undergo 100% factory testing procedures and are certifi ed according to PED 97/23/EC.
The bladder, which is suitable for alimentary purposes, is fi xed at both ends avoiding any possible contact against
the inner tank surface.
ULTRA-PRO pressure tanks offer unlimited service as the bladder is easily replaceable.

Technical features
MIG welded carbon steel body without internal rough spots or sharp edges. Replaceable bladder suitable for use
with potable water. Painted externally with long lasting epoxy powder. Mild steel or stainless steel fl anges for use
with aggressive water.

When the pump starts, water enters the membrane tank as system pressure passes the pressure precharge using
the whole capacity of the tank. Only usable water is stored. When the pressure in the chamber reaches the
maximum system pressure, the pump stops working. The tank is fi lled to its maximum capacity. When water will be
needed again, pressure in the airside will push water into the system. Since Zilmet ULTRA-PRO tank does not water
log and delivers all possible water, minimum pump starts are assured with saving on energy consumption and
increasing the pump life

Click Below For Technical Sheet

Hudson Reed A304 Technical Information


More Information
Manufacturer ID1100030007
Guarantee Length5 Year
Max Working Pressure (Bar)10 bar
Horizontal or VerticalHorizontal
Diameter 630mm
Connection Type1.5"
Capacity300 Litre
Height 660mm

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