Report No FR0336

Dec 1992

I BENEFITS

The identification of maximum acceptable headlosses for the three Water Industry Specifications will give direction to manufacturers designing these service pipe fittings and will give guidance to Water Industry personnel in the specifying and purchasing of such fittings.

The work on headloss in MDPE pipes and the examination of the effects of garden watering on demand will promote the conservative design of domestic systems so that pipe sizing can satisfy the relevant demand.

II OBJECTIVES

To identify maximum acceptable headlosses for boundary boxes, stop taps and ferrules, for incorporation into Water Industry Specifications, WIS No. 4-37-01, 4-23-04 and 4-22-02 respectively.

To compare the headloss for MDPE pipes as given in the WAA `Manual for MDPE Pipe Systems For Water Supply' with that derived from computer software utilising the Colebrook-White formula as tabulated in Report FR 0255.

To determine the effects of garden watering on particular demand patterns and typical domestic pipe layouts.

III REASONS

Water Industry Specifications, WIS No. 4-37-01 Boundary Boxes, WIS No. 4-23-04 Stop Valves and WIS No. 4-22-02 Ferrules, are required to give guidance on maximum acceptable headlosses. Figures that are practical whilst keeping the headloss of these components to a minimum would benefit both manufacturers and the Water Industry.

The tabulation of headloss for MDPE pipes, as identified in Report FR 0255, `Hydraulic Performance of Service Pipe Fittings and Headlosses in MDPE Service Pipes' and the headloss as given in the ` Manual for MDPE Pipe Systems' are known to have certain discrepancies. The significance of these differences therefore needs to be ascertained. Service pipe and small mains sizing are largely based on demand patterns which take little account of the increase in demand due to garden watering. The effects on both pipe diameter and inlet pressure therefore need to be identified.

IV CONCLUSIONS

A maximum acceptable headloss of 3 m.wg was identified for boundary boxes, 1.0 m.wg for screwdown valves, 0.2 m.wg for plug or spherical valves and from 0.4 to 1.6 m.wg for ferrules (dependent on pipe size). All these figures relate to a flow equivalent of 1.25 m/s in pipes from 20-63 mm.

The difference in headlosses for MDPE pipe as derived from computer software based on Colebrook-White and the Design Flow Chart in the MDPE pipe manual is not significant for pipe sizes 20 and 32 mm. However, for 25, 50 and 63 mm pipes, the Design Flow Chart gives headlosses significantly lower than those predicted by the computer model. As the production and reading of flow charts is more liable to error than the computer derived figures, consideration should be given to utilising suitable software rather than relying on the reading of such charts.

Hosepipe usage must be carefully predicted, possibly using network modelling, or domestic systems must be conservatively designed, so that pipe sizing can satisfy demand under the influences of garden watering.

V RESUME

Maximum acceptable headlosses for the service pipe fittings, boundary boxes, stop taps and ferrules are identified for incorporation into the relevant Water Industry Specifications.

Headloss charts and figures derived from computer software utilising the Colebrook-White formula are compared and recommendations are given for their use.

The effect of garden watering on particular demand patterns with typical domestic pipe layout is examined. Suggestions are given for the careful prediction of hosepipe usage and conservative design of domestic systems.

Copies of the report are available from FWR, price £15.00, less 20% to FWR Members.