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Installation of bulk tanks

Introduction

Increasingly dairy farmers are considering the purchase of larger bulk tanks due mainly to changes in milk collection arrangements. The cost can vary considerably, depending on whether a new or second-hand tank is purchased. In either event a significant investment is required.
The bulk tank is an important item of equipment – it is in use every day and must be cleaned and sterilised after each milk collection. Due to the size of the investment involved, the dairy farmer must decide exactly what size and type of tank would best suit the business.

Points that need to be considered include:

  • Size of tank
The tank capacity chosen will depend on herd size, calving pattern, frequency of milk collection and future plans for development.
  • Type of tank
Producers have a choice of water jacket sprayrail tanks, either open or totally enclosed, Direct Expansion (DX) or DX with separate ice builder.

Choosing a bulk tank

Water jacket sprayrail tanks

This is the type most commonly used on Northern Ireland farms. Milk is cooled when chilled water, from an ice bank, is sprayed against the outer surfaces of the tank walls. Between milkings the ice is produced by comparatively small condenser units. In addition, off-peak electricity can be used during the cheap period to make the majority of ice required to keep the milk at optimum storage temperature. The new generation of enclosed ice bank tanks are fitted with a pump to circulate iced water through a plate or tube cooler. This further reduces running costs.

Direct Expansion (DX) tanks

In Direct Expansion tanks milk is cooled by refrigerant plates, which are in direct contact with the outer surfaces of the tank walls. DX tanks cannot store any coolant and subsequently the condensing units must be run when cooling is required which reduces the benefits of off-peak electricity.
The use of an ice builder with this type of tank enables full use of off-peak tariff. In this situation, the milk is pre-cooled before it enters the tank using a plate or a tube cooler supplied with chilled water from the ice builder. An additional advantage is that chilled milk, rather than warm milk, is being added to the already cooled milk in the tank.
The remainder of the cooling takes place in the tank. This also has quality implications. The quicker milk is cooled after leaving the cow the better. This system achieves most of the cooling before the milk enters the tank. It is important that the condensing units are suitably sized to build a full ice bank in the available time, which is not always a full seven hours because many farmers start to milk before the off-peak tariff time has finished.

Milk silos

Milk silos (10,000 litre and upward) are now available and are suitable for the very large producer. These are designed so that they can be installed outside and adjacent to the dairy. All controls and the milk outlet pipe are situated in the dairy. Silos are subsequently more expensive than more traditional milk tanks.

Running costs

Substantial reductions in running costs can be made when an ice builder is used in conjunction with off-peak electricity. Pre-cooling milk using a plate or a tube cooler supplied with mains or well water can also reduce costs and add to the cooling capacity of the tank.

Electricity supply

Before installing a large DX tank, a milk producer should check that the farm electricity supply is capable of operating the larger HP motors installed with this type of unit. These larger motors run for shorter periods than the motors used in conventional sprayrail type tanks. Three-phase electricity is normally necessary for DX tanks with a capacity over 8,000 litres.
There are two main types of condenser unit used with bulk tanks and ice builders:
  •  Semi-hermetic
  •  Hermetic
The semi-hermetic type is more efficient and is more readily repairable than the hermetic type.

Bulk tank cleaning

Automatic bulk tank washers are available and are normally activated by the tanker driver after each milk collection. Most automatic washers on jacket sprayrail tanks use a cold iodophor solution. In addition, supplementary manual washing of these tanks, using a suitable alkali-based detergent, should take place once every two weeks, or more often if necessary.
Most of the large DX tanks now on the market use a hot wash. This normally involves a number of stages:
  •  Pre-rinsing with cold water;
  •  Pre-rinsing with hot water to heat up the surfaces of the tank;
  •  Circulating a suitably formulated detergent steriliser solution at 50oC for ten minutes;
  •  Rinsing with cold water (in some cases chlorinated);
  •  Final rinsing with cold water.
Tanks washed with hot detergent sterilisers should be treated with milkstone remover once per month or more often if required, in accordance with manufacturer’s instructions.
Care should always be taken when handling chemicals. Follow the correct health and safety procedures.

The dairy

When building a new dairy or extending an existing one, consider the following:

Position

Is the dairy:
  •  easily accessible by large bulk collection tankers?
  •  positioned so that the tanker approaches can be kept clean and free from cow traffic at all times?

Size

The installation of a larger bulk tank may require the building of a new dairy or the extension of an existing one. Thought should be given to the position and size required:
  •  Is the dairy large enough for the proposed tank? If not, can the existing one be extended or is a new dairy required?
  •  When all other equipment is installed in the dairy there should be an unimpeded space of 600 mm (2ft) around the tank.
  •    There should also be adequate space between the top of the tank and the ceiling so that the tank can be calibrated or the tank interior accessed if necessary.

Dairy store

Bulk tank condenser units, which are not an integral part of the tank, should be fitted in an adjacent, suitable and well ventilated dairy store. If at all possible, condenser units should not be fitted on a south facing wall. They should be installed in a way which allows them to draw in and discharge adequate quantities of air for efficient operation.
Fitting the condenser unit in the dairy store:
  •  reduces the amount of heat in the dairy;
  •  prevents dust being drawn into the dairy;
  •  avoids attracting vermin to the warmth under the condenser unit in the dairy.

Further information

For further advice contact your local Quality Assurance Milk Inspector or your locally based Greenmount Campus Dairying Development Adviser.
NNote: This leaflet gives general guidance only and should not be treated as a complete and authoritative statement of the law.