Farm Waste Structures: Guidance on Construction, Repair and Maintenance

Sluice valves on steel and concrete circular above-ground slurry stores

Note No: CGN 010, March 2001
Prepared by ADAS National Building Design Team. Funded by The Department for Environment, Food & Rural Affairs.


Figure 1. Double sluice valve - both stainless steel

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Figure 2. Double sluice valve - one galvanised steel, one cast iron

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Figure 3. A simple double gate system - discontinued

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It is vital to maintain all valves in good working order and consider replacing older single sluice valves or simple double gate systems with new double sluice valves to avoid catastrophic failure. Figures 1 and 2 show typical double sluice valves.

The installation of two sluice valves in series on the outlet pipe of a slurry store is mandatory under the Control of Pollution Regulations 1991 Slurry stores built prior to 1991 often only have one sluice valve or the simple double gate system (Fig. 3 ).

Common types of sluice valve

  1. Prefabricated lever operated sluice valves, designed for servicing in-situ, with top access, usually cast into concrete. This is the most commonly recommended current system. There are minor variations in the fabrication of the box, gland and seals. The valves currently used (Figs. 1 and 2) are made from:
  • galvanised or stainless steel by steel store manufacturers.
  • cast iron or a polyethylene casing with a stainless steel gate by valve manufacturers.

The polyethylene valve does not allow top access.

  1. Two earlier designs of prefabricated sluice valves. The most common of these is the glass coated steel valve, with no top access. The other is the simple double gate system of two partially exposed gates made from galvanised steel (Fig. 3). These designs have been discontinued.
  2. Flow regulator ball valves in reception pits that are fitted in addition to the main slurry store sluice valves. The discharge of slurry is automatically shut off by the floating ball when the reception pit is full.
  3. Heavily engineered hand wheel cast iron gate valves, in accordance with BS 5163, that are mainly used in the water and sewage industry. The working pressure is significantly higher than that required for use in slurry stores.

Specifications

A forthcoming revised BS 5502 Part 50 will include specifications for sluice valves on farms. Sluice valves should be fabricated from galvanised or stainless steel, cast iron or, if adequately engineered, polyethylene casing with a stainless steel sluice gate. They should be durable and designed to suit the arduous environment in which the sluice valves have to operate.

Sluice valves should be:

  • Constructed so that all components (e.g. spindle, gate, handle and seals) can be regularly checked, fully serviced and replaced as and when required throughout their lifetime.
  • Constructed so that all points of particularly high mechanical stress (e.g. where the spindle is bolted to the gate) are suitably strengthened during fabrication.
  • Designed to avoid direct contact between the sluice gate and the inner surface of the valve casing and hence provided with a sealing strip between the two faces.
  • Provided with removable top plates to allow easy access.
  • Provided with a grease nipple to apply grease to the actuating spindle for the smooth operation of the sluice gate.
  • Factory tested to withstand a water pressure covering the full range from zero to the maximum working pressure. The maximum working pressure should allow for the freeboard and any possible future extension of the store.

The two sluice valves can be of the same design (Fig. 1) or of two different designs (Fig. 2). It is recommended that at least one of the valves is of the quick action lever type so that closure can be instantaneous.

Construction

  • The two sluice valves can be fitted to the outlet pipe in a trench that leads from the base of the slurry store floor. Both the outlet pipe and sluice valves should have concrete surrounds except for the top part of the sluice valves.
  • Any outlet pipe and valve assembly fixed to the side of a slurry store, or located above-ground outside a slurry store, must be adequately supported. This is to prevent the shearing of the outlet pipe at the side of the slurry store or at the valve joints during the operation of the sluice valves.
  • The two sluice valves should be spaced at least 1.0 metre apart to minimise the risk of long pieces of debris jamming both sluice valves simultaneously.

Operation and maintenance

Safety considerations

  • Both valves must be locked when not in use.
  • Maintenance of the valve nearest to the reception pit must only be carried out when the valve nearest to the store is closed.
  • Maintenance of the valve nearest to the store must only be carried out when the slurry store is empty.
  • Health & Safety Regulations must be observed.

Opening of sluice valves

  • Unlock both valves.
  • Open the valve nearest to the slurry store.
  • Open the valve nearest to the reception pit slowly.
  • Use the valve nearest to the reception pit to control the flow of slurry.

Closing of sluice valves

  • Use only the force necessary to close each valve.
  • Close the valve nearest to the slurry store completely.
  • Close the valve nearest to the reception pit completely.
  • Lock both valves. (The Control of Pollution Regulations require that sluice valves must be locked shut when not in use).

Inspection and maintenance of sluice valves

  • Operate both sluice valves once a month to ensure slurry does not solidify and cause them to seize.
  • Fully inspect both sluice valves annually when the slurry store is emptied and cleaned thoroughly.
  • Make sure that debris does not enter the sluice valves during cleaning.
  • Apply grease to valves to ensure the smooth operation of the sluice gates.
  • Check all fixings are secure.
  • Check for leakage and take remedial action if necessary.
  • Check the satisfactory operation of the sluice valves.
  • For repairs consult the manufacturer or stockist.
  • Fully service sluice valves every five years by engaging skilled personnel recommended by the manufacturer.

Replacing sluice valves

Prefabricated valves made from glass coated steel tend to corrode after a long period of use at the bolted joint of the spindle and the sluice gate. Valves operate under very arduous conditions. Single sluice valves or the simple double gate system (Fig. 3) should be considered as high risk because of the potential for catastrophic failure.

It is recommended that all single valve systems are replaced with double sluice valve systems as soon as practical.

In case of emergency:

  • Have an emergency plan (see Reference 4) in place to deal with any sudden escape of slurry. e.g. identify points where dams can be constructed to catch leaked slurry before it reaches the nearest watercourse.
  • Make sure farm staff understand the emergency plan and know what action to take.
  • Make every effort to close the valves.
  • Contact the Environment Agency immediately on Freephone emergency hotline 0800 807060 (24 hour service).

References

  1. The Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations 1991 (as amended).
  2. British Standard BS 5163. Predominantly key-operated cast iron gate valves for waterworks purposes.
  3. British Standard 5502 Part 50 : Design construction and use of storage tanks and reception pits for livestock slurry.
  4. The Water Code (1998) . MAFF Code of Good Agricultural Practice for the Protection of Water (Paragraphs 12 and 13).

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