Mechanical Pipe Work, Fittings And Valves in Building Construction

Mechanical Pipe work, its Fittings and Valves works described in detail under MEP construction work. It includes pipe erection method, supports both vertical and horizontal, welding, and other fittings and accessories.

Typical drawing for Mechanical Pipework burried underground in MEP installation work

1. MEP Mechanical Pipe Erection

All pipework shall be installed in a neat and workmanlike manner by skilled tradesmen.

All adjacent pipes shall be fitted mutually parallel, all vertical pipes fitted plumb, and all horizontal pipes shall have a continuous fall to low points of 1:240 except where such an arrangement would make it difficult to provide a neat installation. In such cases, a ruling from the Engineer shall be sought.

Generally pipes shall follow the line of walls as indicated on the drawings, including sets around columns as required, and shall be fitted to give a minimum clearance of 25mm from walls, 100mm from floors, and 75mm between pipes.

Where pipes are to be insulated, they shall be fitted in such a manner as to give the prescribed clearance between the insulation and the walls, floors or adjacent pipes.

All sets or pulled bends shall be free from flattening or distortion, and all burred and cut ends of pipes shall be well reamered or filed to ensure that the full diameter of the pipe is maintained. Any sets or pulled bends on UPVC pipework shall be factory fabricated.

No pipe joints shall be embedded in the thickness of walls, floors or ceilings, or in any inaccessible position.

Special care shall be taken before final assembly and closing up to ensure that all pipes are properly cleaned out and free from flux, grit, scale and jointing materials. Ends of pipes temporarily unconnected for any reason shall be closed with plastic caps.

All reductions in the diameter of pipes shall be made by the use of eccentric reducing sockets. Bushed fittings will not be permitted. All tees shall be swept, and all bends long radius, unless otherwise agreed with the Engineer.

2. Pipe Supports in MEP Mechanical Installation

Pipework shall be supported at intervals not exceeding the following:-

(a) Mild Steel Support

Nominal bore diameterVertical pipesHorizontal pipes
15mm 2.50m 1.80m
20 - 25mm 3.00m 2.50m
32mm 3.00m 2.70m
40 - 50mm 3.60m 3.00m
65 - 100mm 4.50m 4.00m
125 - 150mm 5.50m 4.50m
200mm & above 8.50m 6.00m

(b) Copper Support

Nominal bore diameterVertical pipesHorizontal pipes
15 - 22mm 1.80m 1.20m
28mm 2.40m 1.50m
35 - 54mm 3.00m 1.80m
67 - 108mm 3.70m 2.40m
133mm 3.70m 3.00m
159mm & above 3.70m 3.70m

(c) uPVC Support

Nominal Bore DiameterVertical and Horizontal Pipes
Classes B & CClasses D & E
15mm - 0.90m
20 - 25mm - 1.05m
32 - 40mm - 1.20m
50mm 1.05m 1.35m
65mm 1.20m 1.50m
80mm 1.35m 1.65m
100mm 2.50m 1.80m
150mm 2.00m 2.25m
200mm & above 2.40m 2.70m

All pipe supports or clips shall be adequate for the weight to be carried, and shall allow free movement for expansion and contraction.

Pipe supports shall generally be fabricated from mild steel, but ring clips shall be cast brass for copper pipe and UPVC lined for UPVC pipe.

Visible supports in occupied rooms shall generally be split ring clips with back-plate for screw fixing for copper and steel pipes, and moulded plastic clip-in type for UPVC pipework.

Pipework in ceiling voids, plant rooms etc. shall be generally supported from accepted type multiple pipe supports comprising mild steel channel bolted to the underside of the slab, with drop rods and split ring clips. All drop rods shall be fitted with cup washers, nut and locknut. All holes for drop rods shall be drilled, not flamecut. Pipework in horizontal ducts shall be generally supported as for pipework in ceiling voids, but with the channel iron built into the duct walls.

Mechanical pipework method using horizontal support methods in MEP installation work

Where the calculated maximum linear expansion in any straight pipe exceeds 20mm, the pipe shall be supported on rigid welded channel iron frames with rollers and chairs, and semi-circular flat iron hoops to act as pipe restraints and guides.

Pipework in vertical ducts shall be supported from channel iron built into the duct walls, with “U” bolts.

Supports shall be provided either side of heavy items of pipeline equipment such as flanged valves, strainers etc. to avoid any strain on or distortion of the equipment.

3. MEP Mechanical Pipe Welding

All welding on pipework of 80mm and above shall be by the electric arc method, but for pipework of 65mm and below oxy-acetylene welding may be used as an alternative.

All welding shall be carried out in accordance with current good practice by operatives skilled in this trade.

Care shall be taken to ensure that welding material or flux does not project into the bore of the pipes. All welds shall be of good clean metal free from slag or porosity of even thickness and contour, well fused with the parent metal, hammered on completion and finished smooth.

The Engineer reserves the right to have cut for examination 2% of all welds made.

All bends, branches, reducers etc. shall be seamless steel buttwelding fittings. Site fabricated fittings are not permitted.

4. Unions and Flanges in MEP Pipe Installation

Removable joints shall be formed on all steel and copper pipework at intervals of approximately 15 metres or wherever necessary to facilitate dismantling.

Removable joints shall be formed by screwed unions on all pipework up to and including 54mm, and by flanges of the appropriate pressure rating on pipework above 54mm.

All unions shall have two bronze tapered seats. Unions and flanges shall be galvanised when used on galvanised pipework and gun metal when used on copper pipework.

Flanged joints shall be made with an accepted type nickel alloy or composition joint ring.

5. Pipework and Fittings in MEP Mechanical Installations

(a) Black Mild Steel Pipes

Pipework shall be to BS 1387/1967 Heavy Quality, or ASTM A53 Grade B Schedule 40, assembled by means of screwed joints and heavyweight beaded malleable iron fittings, or welded.

Screwed joints shall normally be used on sizes up to 32mm, and welded joints on 65mm and above. On sizes 40mm and 50mm, the choice is at the discretion of the Contractor in agreement with the Engineer.

Screwed joints shall be BSP taper threads to BS 21, clean threaded, pulled up tight, and made with either fine stranded hemp and an accepted jointing compound, or PTFE tape. Excess jointing materials shall be removed after the joint has been made.

On pipe sizes 15m - 40mm inclusive, hot pulled bends formed on site may be permitted providing their radius is not less than 2½ times the internal diameter of the pipe.

(b) Galvanised Mild Steel Pipes

Pipework shall be to BS 1387/1967 Heavy Quality, or ASTM A53 Grade B Schedule 40, assembled by means of screwed joints and galvanised heavyweight beaded malleable iron fittings. The welding of galvanised tube will not be permitted.

Screwed joints shall BSP taper threads to BS 21, clean threaded, pulled up tight, and made with either fine stranded hemp and an accepted jointing compound, or PTFE tape.

Excess jointing materials shall be removed after the joint has been made.

(c) Copper Pipes

Pipework shall be to BS 2871, of one or more of the following grades as indicated in the Particular Specification:

(i) Part 1 Table X Condition ½H

(ii) Part 1 Table Y Condition O

(iii) Part 1 Table Y Condition ½H

Copper pipework up to and including 54mm shall be assembled by means of integral solder ring capillary fittings to BS 864 Part 2. The solder used shall comply with BS 219, and the method of assembly shall be to the fitting manufacturers recommendations.

Fittings of 67mm and above shall be brazed or bronze welded.

(d) uPVC (Pressure Type) Pipes

Pipework shall be to BS 3505, of adequate grade for the service to which it is to be applied, and shall have a tensile strength at 20oC of 34,500 kPa. In all cases particular attention shall be made to the operating pressure when related to the temperature of the medium, and the manufacturers recommendations must not be exceeded.

Joints generally shall be made using an accepted solvent cement of the gap filling type, and following the manufacturers recommended procedures.

Integral mechanical rubber ring joints may be used on pipework of 65mm and above where buried underground. The Contractor shall allow for all necessary thrust blocks where such joints are used.

Care shall be taken with all UPVC pipework to allow for the high coefficient of expansion.

All bends and fittings shall be of the same materials specification as the tube, and shall conform to BS 4346 Part 1.

6. Air Venting and Drainage in MEP Mechanical Work

All pipes shall be run with appropriate gradients to ensure the free release of air and drainage at suitable points on the system.

Where high points occur and Automatic Air Eliminators are not specifically indicated the venting of the pipe shall be effected by the formation of a collecting pocket of not less than 50mm bore and 100mm in length welded to the top of the pipe. Where the main pipe bore is less than 50mm size the connection shall be the same size as the main pipe.

The trapped air shall to be released to atmosphere by way of a 15mm tube carried to low level and terminating with a 6mm bronze vent cock.

Drain outlets shall be provided at all points of the system necessary to empty the system and to facilitate maintenance and repair of the pipework. Collection pockets of ample size for rust, scale or welding pellets are to be provided at each drain point and shall be fitted with a 15mm bronze draining tap.

7. Test Points of MEP Mechanical Pipe work

Pressure and temperature test points shall be provided where required to assist the balancing testing and commissioning and additionally where indicated on the drawings.

Unless otherwise indicated pressure and temperature test points shall comprise a welded socket, into which shall be screwed a selfsealing test plug, with removable cap.

8. Expansion Joints in Mechanical Pipe work

Provision for movement due to expansion and contraction shall be made either by loops, bellows expansion joints, or by change in direction of the pipework. Supports at such points shall be arranged to ensure that all movement is taken up by the loop, joint, or change in direction of the pipework. Where pipework is required to be prestressed for the purpose of reducing expansion stress under working conditions, the extent of the cold draw shall be calculated as half the total expansion.

Expansion bellows shall be of axial pattern or as indicated and shall be provided with screwed or flanged ends as appropriate to facilitate replacement, unless otherwise accepted. They shall incorporate internal liners if required and shall be manufactured from 18/8 stainless steel or other accepted material appropriate to the duty and shall be designed to withstand the test pressure of the system.

Bellows shall be capable of not less than 2,000 complete cycles of movement over the designed working range without failure. Expansion bellows for angular movements shall be arranged as indicated. They shall be provided with tie rods or hinges to take end thrust.

All bellows expansion joints shall be provided with external protection where exposed to damage. For axial bellows this shall comprise an external sleeve.

Bellows shall be installed so that they are not subjected to stresses other than those for which they are designed. Unless otherwise indicated they shall be installed so that they are in their free position at a temperature midway between the high and low limits of normal service.

Mechanical pipework method using vertical support MEP Installation work

Pipework either side of the bellows expansion joints shall be provided with guides to ensure that all movements are taken up in the designed manner. The manufacturer's recommendations shall be closely followed. Guides shall be secured rigidly and shall provide free movement for expansion without undue tolerance.

On mild steel pipework, mild steel anchors capable of resisting the maximum stresses shall be provided and preferably shall be welded to the pipework. Where it is impracticable to weld the anchors to the pipework, cast iron chairs with at least two wrought iron stirrup bolts shall be used, the bolts being provided with sufficient thread to ensure an effective grip on the pipe.

For copper pipework the anchors shall be provided by wide copper straps secured to the pipework in such a manner that the pipe is not damaged. The Contractor shall supply, and fix in position ready for building in, all cleats, brackets and steelwork required for anchor points. Anchor points where secured to the bottoms of ducts or trenches shall be sealed with hot poured bitumen.

9. MEP Mechanical Pipe Sleeves

Where pipes pass through walls, floors and ceilings, sleeves of the same material as the service pipe shall be used. All sleeves shall project 2mm clear of the finished surfaces of walls and floors.

The Contractor shall be responsible for ensuring that the sleeves are in the correct position at the time they are built in.

The space between the pipes and sleeves shall be packed with a suitable flexible material to maintain the fire rating of the walls and floors.

10. Protection of Buried Pipelines in MEP Mechanical Installation

All metal pipework buried underground or embedded in the building structure shall be protected by two layers of a bituminous or petrolatum tape formulated for tropical application.

The tape width shall be 100mm, applied with a 25mm overlap, and the second layer shall be applied in the opposite direction to the first. The minimum cover over buried pipes shall be 600mm for copper and steel, and 900mm for UPVC.

11. Refrigerant Systems in MEP Mechanical Work

Pipework for refrigerant systems shall be of refrigeration quality copper. Joints shall be flanged, brazed, welded or made with soldered capillary fittings.

Pipelines shall be firmly secured and measures shall be taken to prevent vibration weakening joints and connections. Pipework shall be designed and run so that any oil in the compressor discharge refrigerant which passes through the oil separator (where fitted) is carried through the system and returned. At any point where a large quantity of oil may accumulate an oil separator and means of returning the oil to the compressor shall be provided.

Valves required for compressors, liquid receivers etc., shall be of either diaphragm or bellows type or be packed valves complete with a back seating and a seal cap.

Compressors shall not be connected to run in parallel (i.e., with common discharge and/or suction lines). Where, to increase availability, it is required that any compressor shall be capable of working with any condenser or evaporator, cross connections shall be provided and all major plant items shall be valved for isolation.

After erection the whole of the refrigeration pipework shall be pressurised and tested for leaks.

All fittings for use with refrigeration systems shall be suitable quality copper with all joints being made either by flanges, brazing, welding or soldered capillary fittings.

The Contractor shall ensure that the correct quality of brazing or soldering filler rod, together with the correct flux is used for the type of joint with due consideration for the temperature and pressure of the media flowing in the pipework.

12. Compressed Air System in Mechanical Installation

Compressed air systems and their components shall be designed, manufactured and tested according to the relevant Standards and Codes.

All branches shall be taken from the top of the mains. Each branch pipe to compressed air points shall terminate in a standard fitting provided with chained cover.

The system shall be self draining in the direction of flow (where possible) and fitted with drain traps and the necessary isolating and bypass cocks. Each air receiver shall be fitted with its own drain. Fusible plugs shall be fitted as close to compressor outlets as possible to safeguard the installation in the event of the air temperature reaching the lubricating oil flash point.

Fusible plugs shall also be fitted directly into any receivers which are capable of being isolated from the safety valve to prevent an explosion in the event of fire.

The position of the plugs shall be such that their discharge will not cause injury to personnel nor damage to other equipment. Safety valves shall be provided to permit air to escape from the system without increasing the pressure beyond 10% above the blow off pressure when the compressor(s) are delivering their full output and all other valves are closed.

Safety valves shall be fitted with hand operated easing gear. Where reducing valves are installed in a system the low pressure, high pressure and any intermediate pressure systems shall be separately protected by safety valves set to release air as soon as the design pressure of that part of the system is reached.

Safety valve outlets shall be positioned such that escaping air will not cause injury to personnel or damage to equipment.

A pressure gauge shall be fitted to each air receiver, and at each pressure reducing set.

13. Thermometers and Altitude Gauges in MEP Work

Thermometers shall be vapour pressure type with 100mm. dia. dial, chrome bezel, clear acrylic window and black indicating pointer.

Water thermometers shall be provided with separate pocket, and air thermometers shall be back flange mounting. The operating range shall be such that the normal operating temperature is approximately halfway round the scale.

Remote reading thermometers shall be provided where indicated, and shall be back-flange mounted onto a polished hardwood gauge board.

Altitude gauges shall be of the Bourdon tube type with 100mm. dia dial, chrome bezel, clear acrylic window, black indicating pointer and red adjustable pointer. The operating range shall be such that the normal operating pressure is approximately halfway round the scale. Each gauge shall be fitted with lever handle control cock, and shall be calibrated in kPa and Bar.

14. Isolating and Regulating Valves of MEP Mechanical Pipe work

Valves shall be provided as indicated on the drawings and as required for regulation and isolation. All valves shall have a pressure/temperature rating suitable for the intended service.

(a) Chilled Water valves

Isolating valves up to and including 50mm shall be bronze or cast gunmetal screwed gate valves with non-rising stem, screwed bonnet, one-piece wedge disc and cast alloy hand wheel.

Isolating valves of 65mm and above shall be cast iron flanged gate valves with inside screw non-rising stem, bronze trim, wedge disc and cast iron hand wheel.

Regulating valves up to and including 50mm shall be bronze screwed lockshield globe valves, with rising stem, screwed bonnet, metal to metal seat and regulating disc.

Regulating valves of 65mm and above shall be cast iron flanged oblique orifice valves with outside screw, rising stem, copper alloy trim, regulating disc, indicator and cast iron hand wheel.

Double regulating valves up to and including 50mm shall be bronze screwed key-operated oblique globe valves, with rising stem, screwed bonnet, metal to metal seat, regulating disc, double regulating device and four bosses tapped 1/4" B.S.P.

Double regulating valves of 65mm and above shall be cast iron flanged oblique orifice valves with outside screw, rising stem, copper alloy trim, regulating disc, double regulating device, indicator, four bosses tapped 1/4" B.S.P. and cast iron hand wheel.

(b) Valves for Domestic Hot and Cold Water and Fire Protection Services

Isolating valves on the general domestic water and fire services distribution system shall be as for chilled water services, but the final connections to sanitary fittings or ranges of sanitary fittings shall be provided with gunmetal stopcocks to BS 1010. Stopcocks shall be chromium plated easy-clean pattern where exposed to view.

Regulating valves on hot water circulations shall be as for chilled water services.

(c) Valves for Mains Cold Water Services

Isolating valves up to and including 54mm shall be gunmetal screwed stopcocks to BS 1010, with crutch head.

Isolating valves of 67mm and above shall be cast iron flanged waterworks sluice valves, with inside screw, non-rising stem, bronze trim, wedge disc and cast iron hand wheel.

(d) Valves for Gas and Compressed Air Services

Isolating valves shall be full-bore 1/4-turn ball plug valve with stainless steel body, ball and spindle, p.t.f.e. seat, and cast iron lever handle.

Bodies shall be screwed for sizes up to and including 50mm and flanged for sizes 65mm and above.

15. Check Valves in MEP Installations

Valves up to and including 54mm shall be bronze screwed swing pattern, with screwed bonnet and metal to metal seat.

Valves above 54mm shall be cast iron flanged swing pattern, with bolted cover and copper alloy trim.

All valves shall be suitable for mounting in horizontal or vertical pipelines, and shall have a pressure/temperature rating suitable for the intended service.

16. Strainers in Mechanical Installations

Strainers up to and including 54mm shall be bronze screwed Y - type, with screwed cover and stainless steel screen with 0.8mm diameter perforations.

Strainers above 54mm shall be cast iron flanged Y - type, with bolted cover and stainless steel screen with 1.6mm diameter perforations.

All strainers shall have a pressure/temperature rating suitable for the intended service.

17. Ball Float Valves in MEP Installations

All ball float valves fitted on the mains water connection to water storage tanks shall be of the “equilibrium” pattern to minimise the effect of varying mains pressures.

All ball float valves fitted on the pressure boosted supply to secondary water storage tanks shall be of the “Portsmouth” pattern to BS 1212 Part 1, for high pressure use.

Floats for ball-valves may be copper to BS 1968 or plastic to BS 2456.

18. Mechanical Pressure Relief Valves

Pressure relief valves shall be as required by the British Standard relevant to the boiler, calorifier or pressure vessel to which the valve is connected.

They shall generally be of the totally enclosed spring loaded type, with padlock, and with full bore discharge to a safe but visible position to be agreed with the engineer.

19. Mechanical Automatic Air Eliminators

Automatic air eliminators shall be installed only where indicated on the drawing. These shall be of the float operated type with bodies of bronze designed to operate on the maximum pressure and temperature of the service on which they are used.

Each air eliminator shall be preceded by an isolating valve. A 15mm dia. copper pipe shall be run from the discharge connection of the eliminator to atmosphere or to the position indicated on the drawing.

20. Labeling of Valves in MEP Mechanical Installation work

All plant room valves and every circuit control valve shall be provided with a brass, stainless steel or accepted plastic label 75 x 50mm and 1.6mm thick stamped or engraved with a reference number. Wherever practicable the label shall be fixed in a prominent position to identify the valve concerned. Elsewhere purpose-made lightweight steel brackets for carrying the labels shall be welded to the pipework supports adjacent to the valves.

The Contractor shall provide and fix in a glazed hardwood frame, in a position to be indicated by the Engineer, on site, a circuit control diagram showing the positions and numbering of the valves, and indicating valve type and purpose.

On insulated pipework an additional plastic valve label shall be fixed to the outer covering of insulated valve boxes or jackets.


Last Modified: 25-Oct-2018