Api/ei 1585 pdf

View All Publishers. Quality Management. SCC Standards Store. Popular Standards Bundles. Drawing and Drafting. Telecommunications Standards. AWS D1. Means, Inc. Active Only. Complete Document. Guidance in the cleaning of aviation fuel hydrant systems at airports. Detail Summary View all details. Price USD. Need it fast? No one set of conditions can be applied to all systems.

Users of this publication should amend the guidance given to suit local conditions. Local and regional law and regulations should also be reviewed with respect to specific circumstances. Are you an EI Member? If you are not a Member, why not join today and receive all of the benefits of EI Membership? Log In Sign Up Forgotten your password?

A review with all parties involved should be performed to ensure that the agreed commissioning procedure is complete and correct and that personnel are fully competent to carry out the commissioning successfully. Storage tanks should be filled to a level to at least allow circulation of the product.

The cleanliness criteria to be achieved by constructors of depots should be agreed between all responsible parties e. The fuel used for soaking shall be downgraded. Flushed fuel shall be visually inspected until no evidence of manufacturing residue is detected and no colour change noted.

Longer soaking and further flushing may be necessary if the fuel becomes discoloured by the hose. When flushed fuel is found to be acceptable, a minimum of 2 litres USG shall be circulated through the hose assembly. If pressure hoses are taken out of service for repairs e. See also 7. Full design and construction details shall comply with local and national regulations, applicable standards, design codes and take into account industry good practice.

Hydrant systems at airports are one part of the total aviation fuel manufacture, distribution, storage and into-aircraft refuelling delivery system. Each part of the system relies on the correct design, construction and operation of each of the interfacing systems to ensure asset integrity and fuel quality are always maintained for delivery of clean, dry, on- specification fuel into aircraft.

Hydrant systems are the penultimate step in the delivery chain of aviation fuel into aircraft and, as such, all aviation fuel handling system design, construction and operational requirements have to be complied with to ensure that jet fuel quality and cleanliness are maintained at all times. While aviation fuel filtration systems used on equipment for delivery of fuel into aircraft are very effective and efficient, they cannot reasonably be expected to cope with design, construction or operational deficiencies upstream including the hydrant system.

In some countries, hydrant construction completion may require certification approval by a regulatory organisation before it can be put into operation. Once constructed the hydrant system is not readily accessible for inspection or maintenance purposes, hence the need to adhere to good practice in design and construction. Information on hydrant pumps and controllers can be found in 4. Guidelines on the operation of hydrant systems can be found in EI Recommended practice for the operation, inspection, maintenance and commissioning of aviation fuel hydrant systems and hydrant system extensions.

In summary, a hydrant system starts at the inlet to the hydrant pump and finishes with the hydrant pit valve used for fuelling aircraft and low point valve used for sampling and maintenance.

A hydrant system may also include spur lines to a test rig hydrant valve but excluding the test rig and return line , and to a fueller loading facility isolation valve but excluding filtration, meter, hoses and couplings. Hydrant systems may also include fixed cabinet dispensing points. Fuel is delivered under pressure to the fuel hydrant system from the airport fuel depot, via a fixed pipework installation, which is normally buried, to hydrant pits located at each aircraft fuelling position.

These fuelling positions are usually located in the aprons close to the passenger or freight terminal buildings to enable fuelling to take place while the aircraft is being 'turned round'. The aircraft is fuelled by means of one, or in some cases two, hydrant dispenser vehicles. These are connected by flexible hose s to the hydrant valve s , 49 This document is issued with a single user licence to the EI registered subscriber: hector.

Hydrant dispensers see section 6 are fitted with filtration, pressure regulation and metering equipment and are designed to provide the required high standard of quality control, safety and efficiency which should attend all aircraft fuelling operations. At installations involving only a small number of fuelling points, a fixed cabinet dispensing point, embodying filtration, pressure regulation and metering equipment, may be used instead of the hydrant servicer.

Spur 1 Terminal building Spur 2 Tank Spur 3 Pump Filter Terminal building Low point drain Spur 4 Hydrant pit valve Figure 6a: Simple hydrant system design with spurs dead ends 50 This document is issued with a single user licence to the EI registered subscriber: hector. The system is straightforward and low cost, but the design is inflexible.

Due to the 'single feeder line' concept future extensions or major uplift changes in the headers are difficult to accommodate without an expensive change of pipe dimensions. System commissioning or maintenance by flushing and pigging is complex due to the 'dead end' piping configuration and the required application of reducers. Figure 6b shows a more advanced hydrant system layout.

The hydrant system headers are looped, divided into segregated sections and in this example, fed from two feeder lines. The main advantage is the overall system flexibility with reference to commissioning, flushing from one tank to the hydrant and back to another tank, maintenance, pigging and future capacity increase. The design of a hydrant system will be dependent upon a number of factors including traffic forecasts, airport development programmes and aircraft types and design trends.

It is therefore important at the evaluation stage to collect and analyse all relevant data to provide a sound basis on which to establish design parameters. Where a new airport layout design is still at a conceptual stage but a hydrant system design is required at this point, ongoing close working relationships with the airport development consultant shall be maintained to ensure that layout changes do not impact on the hydrant system.

Examples include apron, taxiway or runway realignments, aircraft parking position realignments, building and foundation realignments, tunnel and underground basement realignments, storm water drainage channels and other underground services which may impede access to low points or valve chambers or may damage already laid hydrant pipes during later construction. The system should be designed to ensure that fuel may be delivered at the aircraft coupling at the required pressure and flow rate from any position along the hydrant.

Operational details on these issues can be found in EI In terms of hydrant flow velocity, there is a balance between the requirement to minimise surge pressure, the need to maintain self-cleaning flow regimes within the hydrant, and achieving the required fuel delivery rates for all expected throughput scenarios over the operational life of the hydrant system. Hydrant systems may be subject to hydraulic shock pressures or surge pressures when fuel supply to the aircraft is shut off e.

Hydrant system surge pressures are dependent upon fuel velocity in the pipe and the hydrant configuration and length in relation to valve closure time. The use of surge suppression systems shock absorbers in hydrant systems should be avoided, as the accurate calculation of their capacity is difficult and ongoing maintenance is challenging.

The direction of flow may not be as simple as first thought, especially for complex systems with multiple loops and multiple feeders. An understanding of flow directions and velocities will ensure low points are in the most effective positions.

Hydraulic flow analysis and modelling is likely to identify areas of potential risk of particulate matter accumulation. The modelling should include analysis at different flow rates that reflect the realistic initial throughput volume, growth volumes and maximum design volume.

It should be recognised that hydraulic analysis requires specialist knowledge. Larger diameter feeders in particular are installed to allow for future growth.

These initially result in lower velocities which may lead to problems later as settled-out particulate in the pipe may be moved as flows increase. However, proper initial cleaning and efficient into-hydrant filtration should overcome this problem. If double feeders are built see Figure b , each one sized for initial volumes and short-term increases, and which can be used singly in the early life of the system, higher flow velocities will ensure a measure of self-cleaning.

As volumes increase and the velocity in one feeder becomes greater than is desirable, both feeders may be used. Such a design will allow greater flexibility in operations and provide for loop flushing but is more costly to build and may not always be feasible.

The hydrant system or system extension should be designed to aid the use of pigs or other methods, such as water blasting, for cleaning for procedures see EI Guidance in the cleaning of airport hydrant systems.

This should include the inclusion of suitable spool pieces and double block and bleed valve isolation located in convenient positions such as valve chambers or appropriate above-ground locations. Where pigging is intended, all valves and pipe fittings that the pig will have to pass shall be full bore diameter. Bends shall be long radius and all equipment within the bore of the pipe should be removed e.

Any changes in pipe diameter should ensure they will allow free movement of the pigs. Soft foam pigs are very flexible and may extrude themselves into smaller pipes, low point sumps or risers along the main line. Where future pigging is being considered, sumps or junctions with smaller diameter pipes should include a 'T' bar to prevent the pig becoming trapped. Consideration should be given to the provision of suitable pig launching and receiving traps or arrangements, such as on a temporary basis.

As hydrants are generally very long, a continuous downwards slope would result in the pipe having to be installed at considerable depth at the far end which is not usually achievable given the typical ground conditions at most airports.

Therefore hydrants are generally installed with down and up sloping sections. The up sloping sections shall be fitted with high points to remove any trapped air. It is important to ensure that continuous slopes to low points are provided to avoid pipe suppression due to poor pipe bedding or back filling applications, which will inevitably create unintended low points. Where the hydrant pipe is required to go over or under an obstacle such as a storm water drain or pipe, sewage system or other buried service, a low and a high point will be created.

Each of these shall be included in the routine low and high point checks. Riser lateral pipes shall have a continuously positive slope towards the entry point into the pit box to avoid inadvertent low points. Where pipes include loops or ring mains, the fuel flow direction may not be in the expected direction.

Wherever there is a low point in pipework, these low points shall be fitted with low point sampling valves for regular aviation fuel quality control testing. Low point pipework is usually relatively small diameter pipe e. Designated low points shall be designed to incorporate a sump into the mainline, into which any solids can fall and be extracted through the low point pipe see Figure 7.

Such 54 This document is issued with a single user licence to the EI registered subscriber: hector. Simply spudding a small diameter pipe into the bottom of a large diameter mainline is not acceptable, as the fuel velocity and momentum in the mainline will carry any water, particles or sediment directly past the low point. Figures 7a and b: Types of typical low point arrangement In cases where small diameter pipework, such as for low and high point drains, is buried, it should be at least Schedule 80 pipe, to ensure transmitted surface loadings do not weaken the pipe, and fully externally coated, to prevent external corrosion.

Low point drain valves should be located in hydrant pit boxes. If the low point drain is located in a valve chamber, the flush valve should be accessible from the surface without the need for confined space entry.

The same design considerations as for low points should be applied. High point flush valves and dry break connectors shall be installed in pit boxes. If the high point is located in a valve chamber, the flush valve should be accessible from the surface without the need for confined space entry. Each valve shall be rated for the hydrant pressure. The dry break coupling shall be designed to relieve trapped pressure to allow easy connection and disconnection of the hose coupling.

Different schedule pipe may be necessary depending on loading. Pipe shall be externally coated or wrapped e. Pipe shall be lined internally with an epoxy lining material that complies with EI Performance requirements for protective coating systems used in aviation fuel storage tanks and piping.

If stainless steel pipe is considered for buried pipe, it should be noted that it may still corrode externally and therefore require an external protective coating see previous paragraph. Measures to prevent electrolytic corrosion developing between stainless steel and other materials such as steel valves will also be required. Overall, the use of stainless steel for buried pipe is not advantageous over carbon steel pipe.

See EI Pit valve positioning is a complex task and expert advice from an experienced hydrant system designer should be sought. This is to ensure that the finished position of the hydrant pit valves relative to the aircraft parking position is suitable for use with the aircraft types being refuelled.

Usually there would be two hydrant pit valves on each parking gate; however, if multiple aircraft types and sizes are to be parked on the one gate, more hydrant pit valves may be required. Generally hydrant dispenser uplift hoses are approximately 12 m 40 feet long, although some dispensers may be fitted with a swinging boom which will add another 3 to 4 m 10 to 13 feet. Aircraft fuel panel positions vary considerably between aircraft types and the relative positions of fuel panels, hydrant pit valves and dispenser hose lengths are critical.

Hydrant pit valves should not be located under engine nacelles, close to engine inlets and exhaust or close to aircraft vents. Consideration should be given to avoiding hydrant pits being located in the access area for the aircraft baggage door, to minimise the risk of collisions with hydrant pit couplers. Once the concrete is laid, the position of the hydrant pit valve is fixed. Terminals with moveable air bridges provide some flexibility but those with fixed air bridges provide very little room for error.

Even a re-alignment of 'just a couple of degrees' of the aircraft parking centre line or nose wheel parking position can render the hydrant pit valve position unsuitable for use. This is due to the length of the aircraft and the sweep of the wings relative to the nose wheel position. Some airports operate turbo-prop, narrow body and wide body jets on the same parking gate and may even operate half-gates where two narrow bodies are placed on a wide body position. Pits shall be capable of accommodating the equipment detailed in 5.

Pit boxes shall be at least mm 18 in. Larger diameter pit boxes are available; smaller diameter pit boxes are not acceptable for reasons of operability. Refer to EI 3. The design of covers shall be such that they can be safely lifted by one person.

Materials used for pit covers shall not produce sparks when struck. Covers shall be designed to prevent them being carried away by jet blast or propeller vortex e. A pit lid tether shall be connected to the pit box only. If the pit box is fitted with a hinged lid, the lid shall be so orientated that, when open, it does not cause the lanyard, where used, to become snagged.

Pit boxes shall ensure that they provide containment of liquid. This includes where riser pipes enter. Seals around riser pipe entry points should be readily inspected and replaceable in service. High loadings can be imposed on hydrant pit boxes from aircraft wheels, tugs, other service vehicles or from settlement or movement of adjacent aprons. To prevent transmission of these loadings to hydrant risers to which the hydrant pit valve is fitted , each hydrant pit box should be effectively isolated from its hydrant riser by means of a sealing arrangement that can accommodate both lateral and vertical differential movement.

Pit boxes should be installed so that they project at least 25 mm 1 in. The concrete should finish flush with the top of the pit box so that ground service equipment, especially stabiliser feet, cannot catch the edge of the pit box.

It is recommended that, to facilitate maintenance, an isolating valve be installed between the riser flange and the hydrant pit valve. Spur lines to hydrant pit locations shall be designed so that water will drain back to the main line.

If this is not possible, e. The hydrant pit assembly arrangement shall conform to the latest edition of EI See schematic in Figure 8.

See the latest edition of EI , 3. The lanyard shall be of fire-resistant material of adequate strength to enable the valve to be operated remotely should an emergency occur during the fuelling operation and shall be a highly visible colour, such as red.

The lanyard shall be a minimum of 5 m 16 feet in length. The end attachments shall be permanently and securely connected to the lanyard. A means of storage of the lanyard when not in use shall be provided.

If the lanyard is permanently connected to the chassis, it shall be electrically isolated. This clearance is required to ensure that when a coupler is attached to the hydrant valve, the underside of the coupler elbow and hose does not touch the top of the pit box and cause uneven stress on the pit coupler lugs. Design and construction of these chambers should include at least the following: a Consideration of whether the chamber is cast concrete or of prefabricated design.

For airports on land below sea level or where high natural ground water levels exist, special design and construction techniques for waterproofing may be required e. Permanent suction piping, which is accessible from the valve chamber cover, may also be required to allow accumulated water to be removed. Valve chambers are confined spaces and will be a hazardous area Zone 1 see Figure 9.

Figure 9: Hazardous area zones for valve chambers and hydrant pits 5. These have the ability to adjust to fuel pressure and flow rate demands and shut off when not required. These offer the benefit of reduced electricity consumption and reduced electrical maintenance requirements, while providing acceptable fuel flow characteristics throughout the hydrant system. If there is a recirculation line between the hydrant pressure header and the pump suction header then reverse flow shall be prevented.

Jockey pumps should not operate when main pumps are operating. Jockey pumps may also be used for automated hydrant integrity testing systems. PLC systems should include safety or interlock controls with the sensing devices used to trigger alarms and shutdown systems. Examples on a hydrant system include pump over-temperature protection, flow sensors and filter differential pressure transmitters.

There are many other depot inputs which include tank inlet and outlet valves that cannot both be open at the same time, or tank outlet valves which cannot be opened until fuel density and release information is loaded, or hi-hi levels that will activate alarms, shut down tank valves and shut down transfer pumps. HP, VC10 and painting with a warning pattern or uniform colour around the feature. Confined spaces, such as valve chambers, shall include signage warning of restricted access and confined space entry procedure requirements.

A contact telephone number for the hydrant operations control room should also be included. Valve selection includes consideration of their suitability for automated integrity testing systems and whether they will allow the passage of a pig. The first step in the process, as described in 5. In addition, cathodic protection CP of the hydrant system shall be installed. Corrosion is an electrochemical process involving the movement of electrons from the elemental iron i.

The rate of corrosion will increase in the presence of salty or acidic water. The process of corrosion can be stopped by applying either a separate metal anode that preferentially corrodes sacrificial anode , or by application of an external d. The impressed current design offers the advantage of greater simplicity and reliability, although this is not suitable for protecting stainless steel, and is therefore preferred for hydrant systems.

As sacrificial anodes deplete over time, they will eventually require replacement, therefore they need to be located in an area where they can be accessed, i. Note that impressed current anodes should not be located too close to the hydrant as interactions can occur. Similarly, CP test points should be easily accessible to facilitate maintenance.

Where the hydrant design allows for future extensions, the CP system should also be designed for expansion e. Appropriate insulation is required where electronic equipment or motor-operated valves are installed, to prevent interaction with the CP system.

Each CP system requires site-specific design. An effective CP system design is complex and should be undertaken and maintained by CP specialists. The routing of cable trenches may coincide with the routing of hydrant pipe.

Consideration should also be given at the design stage to the adequate provision of strategically-positioned connection points for future pressure testing.

Specific details should be sourced from recognised vendors of aviation fuel hydrant integrity testing systems. Using more than one technique is often advantageous. Each system requires an understanding of the site-specific baseline conditions against which to measure any changes, i. In order to confirm that the automated hydrant integrity testing system functions correctly, simulated leaks will be required to be created in each hydrant system section at least annually. Detail of the test procedure to be used should be obtained from the system supplier.

For further details of automated hydrant integrity testing systems, and their periodic functional testing, see EI Consideration should be given to whether the ESD system is either hard wired or wireless. Regardless of the system used, it shall be fail-safe i. This is to ensure that ESD button activation is investigated and to confirm it is safe to restart the hydrant pumps.

For larger airports with multiple hydrant systems and associated pump sets, the ESD system for one hydrant system may not need to shut down the other hydrant system s. Additional ESD systems should be fitted which automatically shut down the hydrant system when earthquakes are sensed. All emergency stop signage shall be permanently and legibly identified and meet local and national standards.

The ESD system should be configured such that it is possible to diagnose which stop button has been activated. For large hydrant systems, sets of ESD buttons may be grouped into sectors such that if there is activation or a failure in one sector 62 This document is issued with a single user licence to the EI registered subscriber: hector.

Designers should beware of only shutting down section valves associated with a particular ESD rather than the pumps and into-hydrant block valves , as an operator may see something in the distance and activate a button local to them. ESD buttons may be fitted in supplying and light vehicles of the into-plane operator and hydrant operator, and be identified if activated. Wind, rain, cold, heat, humidity, dust etc, can all cause difficulty with processes such as welding.

Despite these challenges, it is critical to ensure the maintenance of strict cleanliness standards throughout all phases of construction 'clean-build'. This may include specialists in welding, hot tapping, coating, CP etc. This supervision should be independent of the construction contractor. Apron sites are often congested and so it is typically advantageous to prefabricate pipework, spool pieces, low point drain assemblies and other components off-site. All prefabricated components and pipework shall be effectively protected against the ingress of dust, dirt and rain water while in storage and transport.

A welded joint map shall be maintained which will also include identification of the person who undertook the weld. All welded joints shall be X-rayed to confirm integrity including those in valve chambers. The epoxy lining interior coating and the exterior corrosion protection material shall be cut back by at least 25 mm 1 in. Contamination can be minimised by the use of plugs to prevent the debris being forced back up the line.

Immediately prior to final position alignment and welding, each section of pipe or fittings shall be visually inspected to ensure they are clean and dry and any plugs are removed. In case of an unsatisfactory inspection, the pipes shall be thoroughly cleaned and dried before being installed into the open trenches and at their final position.

At least the first welding pass should be by using a metal inert gas method, as this method is much cleaner, produces less splatter, welding scale and products of combustion soot , and generally has better heat control and produces a smoother root bead weld when compared with flux coated metal arc rods. The wrapping should then be tested using a Holiday Tester, in accordance with NACE SP Discontinuity holiday testing of new protective coatings on conductive substrates.

It is important that pipes are backfilled as soon as possible after satisfactory holiday testing to avoid potential damage to the external wrapping. Pipes shall be laid on a firm support base bedding to ensure no low points are induced during the back fill and compaction process.

Before backfilling commences, it should be ensured there is no construction debris pipe off cuts, welding wire or rod ends, concrete, stones, etc.

The integrity of the pipe external coating should be checked using a Holiday Tester to confirm there has been no damage to the coating after placement and tie-in work. Placement of the backfill should be in layers and each layer individually compacted to minimise the stresses placed on pipe or control system wiring or other services in the trench.

Where the back fill material is lean mix slurry concrete, ensure vibrators do not damage the pipe external coating material. The use of pipe marker tape should also be considered. During and immediately after pouring of concrete verify effective vibration. Pipe lengths shall be positively capped or plugged at all times when they are not being worked on. The ends should be closed during all phases of construction, particularly during rainfall where flooding of the lines may occur, and at the end of any working period.

The dirt can required and should be carried out until a clean be vacuumed out by a suction device such as the condition is obtained. Precautions should be taken to ensure that the dirt being blown back does not pass the entry point 6. As the nozzle is small in was designed and successfully used to clean out size, the volume of water required to propel it forward extensive sections of the hydrant in pipes down to and blow back the dirt is relatively small but at a high 40 cm 16 in. The sledge was fed along the line with pressure.

After the nozzle has travelled the maximum a CCTV camera following it to observe and record the distance that it is intended to travel, it may be retracted results on videotape. The dirt and debris continue to be blown back as 6. A tandem powerful suction hydrant pit valves and lowering the level of fuel if device can be used.

The sledge 6. This may be caused by fine to be sufficient to work from stand to stand. Such debris may be pumped out by lowering a any ferrous material and a suction hose to pick up non- hose or metal lance down the riser after removing the pit ferrous material and water, where present.

The hose was valve. If a metal lance or equivalent is used, care is connected to a pump with good suction characteristics, necessary to avoid causing damage to the internal lining in this case the pit servicing vehicle, with a coarse of the pipe. It is usual to flush at least twice, or preferably commencing the flushing. If the fuel in the tank s to be three times, the capacity of the section cleaned into a used is from more than one batch, a full certification test tank vehicle to ensure that quality control requirements should be carried out on the product in each tank are met before returning the section to service.

The time involved to establish a quality baseline against which that the line can be made available to carry out such the quality of the flushed fuel may be compared.

As mentioned in 6. This method has 6. This will establish a Satisfactory cleaning will have been achieved when 'baseline' for the level of solids in the fuel against which colorimetric results are not more than two dry colour results of tests carried out on the hydrant system may be numbers between the fuel entering the system and the measured.

This may be done by using a suitable spool piece 7. After each main weld is installed when, and if, needed. The reverse nozzle mentioned in strict attention to ensuring that water and solid materials 6.

This is in addition to the inspection of welds open end of the pipe. It will be necessary to take and other construction features by appointed inspectors.

The should be cleaned thoroughly and care exercised to ends should be closed during all phases of construction, ensure that no foreign material enters the pipe string. If particularly during rainfall where flooding of the lines proper care has been exercised, most of the debris may occur, and at the end of any working period. Blowing out with 7. Where it is necessary to carry out the this is not always successful, other means of cleaning pipe end preparation on site, pipe stoppers should be may need to be employed.

Equipment 7. All such materials must be meticulously removed before installing the equipment. Ensure that the pit box is dry before removing ensure that no depressions that would form unwanted the flange prior to installing the pit valve. If approved laboratory to establish its suitability for the presence of such material is detected, appropriate aviation use.

If the fuel used in the flushing is from one action must be taken, see Section If fuel from more than one batch microbiological growth, it is essential that all tanks are is used, a full certification test should be carried out on checked frequently for bottom water and any found the product.

Fuel that fails to meet the requirements of removed. It is important that special attention is paid If commissioning is not Cleaning should be done just before the connection is carried out correctly, debris left in the system will lead made.

Debris and other detritus may A temporary mesh strainer inserted at the start of provide an environment to trap moisture, which may the new section may provide an indication of the lead to microbiological growth problems. Therefore, it condition of the old section of the hydrant. However, is essential to ensure that the system is clean before the means to easily remove the strainer should be placing it into service for fuelling aircraft.

It is also important to drain and dry the system During the construction itself, stagnant sections of completely after hydrotesting of the lines, if this is the old hydrant system should be flushed out carried out with water.

After draining from all the low periodically to prevent water accumulation and fungal points, further drying can be carried out by using dried, growth. If the existing low points cannot achieve this, oil free, compressed air. The dew point of the exit air then alternate methods covered elsewhere in this should be almost the same as the air entering. This publication will have to be adopted.

Guidance on out and prior to placing the system in service. It is preferable to carry out the flushing without The fuel in the old system, that is to be connected stopping the flow. In this case, flushing into vehicles or other flushing. However, 'witches If this is not possible, suitable fixed temporary should be developed.

Such a plan should contain not tanks or tank vehicles, preferably road bridgers, need to only the operational features, but also set out the be mobilised. Pit valves should be removed during the The direction of hoses may be connected to pit valve risers at the end of flushing on complex systems should be decided with the leg to be flushed.

See 6. Ball valves, or similar fast acting valves should be used to This may be done place during the flush, but care should be taken not to by using a dip rod such as a length of reinforcing bar, create surge pressures when closing them. If more than a trace of water