Description

CEM – Expansion Tanks

An expansion tank is an important part of any pressurised water system that includes a pressure-controlled or jet pump. Some modern computer-controlled pumps may not require an expansion tank. Fitted close to the inlet line of the hot water system, the expansion tank acts as a pressure buffer, ensuring control of water pressure in a closed system. Without an expansion tank, the system is liable to suffer from pressure stresses.

An expansion tank is much the same as an accumulator tank however the pressure of the membrane should be set at a level according to factors listed below. The main difference is that the tank stores the water pressure to avoid the pump system cycling (switching on and off frequently). An accumulator can also be used before the pump system to act as a buffer tank (sometimes referred to as a header tank)

Our range of expansion tanks are supplied in either polished stainless steel and white painted steel, however, we can paint them in any colour that you require, just get in touch with us

FAQ’s

Why do I need an expansion tank?

Heated from 10 to 60ºC, water expands in volume by about 2%. The calorifier expands too, but not as much as the water. A litre or more of hot water may need to escape from your calorifier as it heats up. A normal accumulator tank can absorb this excess water, provided it is of sufficient size. In the process, hot water will flow back into the cold water line. If hot water back-flow cannot be tolerated, a non-return valve may be fitted in the inlet line to the calorifier.
The expansion water will then be discharged through the calorifier temperature/pressure relief valve, which opens at the maximum working pressure of the calorifier .
To avoid water wastage, to prevent unnecessary stress on the calorifier , and to avoid build-up of deposits in the relief valve, an additional expansion tank may be fitted in the inlet line to the calorifier

Where do I fit an expansion tank?

The expansion tank should be fitted in the cold water feed line to the calorifier , between the non-return valve and the calorifier

How do I install an expansion tank?

Tanks may be installed in a vertical or horizontal position. The tank may be secured by stout strapping or by stainless steel bands, or it may be mounted in a wooden cradle. A special bracket mounting kit is included for the three smallest sizes The steel tank casing is robust, but care should be taken during installation not to scratch, dent or puncture the tank

What size of accumulator tank do I need?

The required capacity of the expansion tank depends on:

• pump cut-out pressure
• the difference between the pump cut-out pressure and the opening pressure of the relief valve in the hot water tank or calorifier
• the volume of stored water in the hot water tank or calorifier

All three of these factors are taken into account by a fairly complex calculation.
To calculate the expansion tank volume you require, we advise that this should be done by a plumber or the installer who has access to the entire system planned and can ensure that the system is safe.

At what pressure should I set the accumulator tank?

The pressure in the tank is adjusted by means of the air valve in the closed end. The tank is supplied with an internal pressure of about 2.8 bar (35 psi). Reduce this pressure to 2 – 3 psi below the cut-in pressure of the pump (refer to pump instructions for details). This pressure adjustment is best done before the installation of the tank, using a car-type pressure gauge to determine when the required pressure is reached, as follows:

1. Depress the central pin of the Schrader valve with your finger, to release gas
2. Release gas a little at a time, until the pressure is correct
3. If you release too much gas by mistake, air may be pumped back in with a hand – or foot-pump

If the tank pressure requires adjustment after installation, ensure first that the pump is switched off and that an outlet is open so that there is no pressure in the system. Then regulate the pressure as indicated above
Check the accumulator tank performance in this way every 6 months, and adjust the pressure if necessary

Winter precautions

To avoid the risk of frost damage, drain all the water from your pressurised water system, before winter lay-up. Switch off the pump, open all outlets until the flow ceases. This will allow water to be expelled from the accumulator tank. Drain all remaining water from the lowest point in the system. Remember to drain your calorifier from the bottom (cold-water inlet)

CEM Pumps and blowers page for accumulators

About CEM Pumps and Blowers

Established in 1970 C.E.M. elettromeccanica S.r.l. has been a leading manufacturer of electric pumps and DC motors primarily focussed for use in the maritime sector
In the 48 years, we have been making motors and our constant expansion in the national and the international markets have resulted in the broadening of our extensive product range

…highest quality materials…design…innovative production processes…remarkable lifespan…

This makes us the ideal partner for large and medium-sized boat builders of pleasure, fishing and military vessels.

Our extensive range now includes:

• DC and AC electric pumps
• Belt driven pumps, with manual or electromagnetic clutch
• hydraulically driven pumps
• water pressure systems
• centrifugal and axial blowers
• diesel driven pumps
• manual pumps
• DC motors

Our commitment to using the highest quality materials used, the special care invested in the design and in the innovative production processes we adopt, we are able to offer excellent performances and a remarkable lifespan of our products exactly what you need when our product can offer extra hours of safety when in difficulty

The CEM factory is based in Nonantola close to Modena in Italy, and is a family-owned business with generations of experience in the manufacture of pumps, blowers and electric motors

All of our products are built to standards that are in accordance with classification and certification can be obtained from each of the bodies: Bureau Veritas, Det Norske Veritas (DNV), Lloyd’s Register and RINA