GB2354014A

GB2354014A - Drainage system comprising pipework and a rainwater outlet capable of inducing syphonic flow

Info

Publication number: GB2354014A
Application number: GB0028266A
Authority: GB
Inventors: Peter Noel Williams
Original assignee: Alumasc Group PLC
Current assignee: Alumasc Group PLC
Priority date: 1997-01-10
Filing date: 1997-01-10
Publication date: 2001-03-14
Anticipated expiration: 2017-01-10
Also published as: GB2354014B; GB0028266D0; GB2321067B; GB9700387D0; GB2321067A

Abstract

A drainage system comprises pipework (18) and rainwater outlet (10) capable of inducing syphonic flow, wherein a tail piece 68 of the outlet 10 is connected to the pipework system via a syphon break, such as an air inlet or a portion of the pipework having an increased diameter.

Description

2354014 HEAD-INDUCED SYPHONIC RAINWATER OUTLET This invention relates to

outlets for draining rainwater from surfaces such as flat roofs or paved areas, or from gutters, such outlets either being stand alone products or for use with an associated pipework or gutter system.

Our UK patent specification no. GB 2285460 discloses an outlet comprising an upwardly open sump for receiving water from a gutter or a surface to be io drained and accumulating a head of water; an inlet passage extending upwardly from towards the bottom of the sump for discharging the accumulated water and a syphonic outlet passage extending downwardly from the upper end of the inlet passage. In a preferred form the inlet passage concentrically surrounds the outlet passage. The sump and arrangement of passages is effective in inducing syphonic flow in the outlet passage when only a small head of water exists in the gutter or on the surface to be drained.

The disclosed outlet design is however hydraulically inefficient. Consequently, flow rates through the outlet are low until syphonic flow is established, whereupon there is a sharp transition to much higher flow rates. The outlet will therefore perform effectively in draining a given area using a pipework system of smaller capacity than is possible with non-syphonic outlet designs. However if the pipework is not designed at the outset to withstand syphonic operation, the sharp transition to syphonic flow at only moderate levels of rainfall can cause problems, in extreme cases even failure of pipes, their mountings and joints. The sharp transition in flow regimes may result in surging of flow during light rainfall conditions whereas sustained heavier rainfall intensity will induce a constant syphonic condition.

The present invention aims to mitigate these problems and accordingly provides a drainage system comprising pipework and an outlet capable of inducing syphonic flow, the outlet having a tail piece connected to the pipework via a syphon break, whereby the pipework is not subjected to syphonic flow. This will ensure that the pipework does not experience the higher stresses associated with syphonic flow, whilst at the same time most if not all of the benefits of the high performance syphonic outlet are retained. The syphonic outlet and syphon break could, for example, replace a 2 conventional non-syphonic outlet. The overall performance of the system will be improved without any danger of over stressing the existing pipework designed for non-syphonic operation.

A convenient way of forming the syphon break is for the tail piece to be non-sealingly telescopingly received in an upper end of the pipework. Alternatively, an air inlet can be used, or a chamber or portion of the pipework having an increased flow cross section can be provided to act as the syphon break. 10 In a corresponding aspect, the invention comprises a method of connecting a rainwater outlet capable of syphonic operation to a pipework system, comprising the step of forming a syphon break between the outlet and the pipework system. 15 Illustrative embodiments of the invention are described below with reference to the drawings wherein:Fig. I is a cross-sectional view of a first outlet embodying the invention and 2o Fig. 2 is a cross-sectional view of a second outlet embodying the invention. The rainwater outlet 10 shown in figure I comprises a body 12 of spun aluminium or stainless steel defining a sump 14 in which a head of water may accumulate. A spigot 16 leads water away from the sump into pipework 18 to 25 which the spigot is connected by a standard flexible pipe sealing joint 20 and worm drive clips 22. The body 12 is secured in a hole in a roof deck 24 by an upper flange 26 provided with screw holes 28. A bituminous membrane covering the deck 24 is secured and sealed to the flange 28 by a clamping ring (not shown). The flange 28 also has a PVC coating to which PVC single ply 30 membranes can be welded or adhered. A domical grating 30 serving as a leaf and stone guard is secured as a push fit in a widened mouth 32 of the surnp14 which joins the flange 26 and body 12 to form a supporting shoulder 34. The grating 30 is frictionally retained by an 35 0 ring 36 mounted in a recess 38 cast into the rim 40 of the grating 30. The grating 30 is a standard component including a depending vortex suppression skirt 42 as described in our patent application no. GB9623909. As shown the 3 skirt 42 is supported sufficiently far above the body 12 so that flow through the outlet 10 becomes syphonic before the skirt depends into the water stream. The skirt 42 therefore has very little if any influence on flow performance of the outlet 10. However if desired the skirt can be supported at a lower level so that it depends into the water stream acting to reduce air entrainment and to establish syphonic flow at lower flow rates than in its absence. Bolt holes normally used to secure the standard grating 30 to a cast metal body are blanked off by plastics inserts 44.

io A cap 46 is suspended concentrically above the spigot 16 on a stud 48 screwed at its upper end into a threaded inset 50 cast into a boss 52 formed at the centre of the grating 30. The floor of the sump is dished inwardly to form a smoothly radiussed crest 54 surrounding the spigot 16. The transition region between the sump side walls and floor is also smoothly radiussed.

A smoothly radiussed lip 56 of the cap 46 forms the uppermost point of an inlet orifice 57 from which a discharge passage leads upwardly over the crest 54 to a discharge end formed by the spigot 16. The underside of the cap 46 is vaulted at 58 and has a central downward protruberance 60. The discharge passage thereby defined between the cap underside and the crest 54 has a lazy s profile as indicated by arrow 62. The lip 56 lies a small distance above the crest 54.

Comparing figures I and 2 optionally the flange 26 may be replaced by a smaller diameter flange 25 by which the outlet 10 can be fixed beneath a discharge hole formed in a flat bottomed gutter 11. The flange 25 is secured and sealed to the hole periphery by bolts 29 and a gasket 27.

The body 12 of the outlet 10 shown in figure 2 has a flat bottom and the crest 54 is formed in a UPVC insert 64 retained as a snap fit in the bottom of the sump 14 by three dimples 66 pressed in the body side walls (only one dimple 66 shown). The insert 64 is bonded to a threaded plastics socket 66 for retaining a tailpiece 68 formed from flexible plastics hose which extends into the adjacent pipework 18. The flexibility of the hose 68 allows connection to curved pipes.

4 If desired, the insert 64 and socket 66 can be sealed to the body 12 by mastic, adhesive or potting compound. The joint between the spigot 16 and the pipe 18 can remain unsealed and acts as a syphon break by allowing entry of air. However, usually the spigot 16 and pipe 18 will be joined by a sealed connection such as 20 shown in figure 1. It is then unnecessary to seal the insert 64 and socket 66 in the body 12. The increase in flow passage diameter at the downstream end of the hose 68 where it enters the pipe 18 will also act as a syphon break. Alternatively the sealed connection 20 or pipework to which the inlet 10 is connected can incorporate an air inlet, for example a one- io way valve. As mentioned above, other forms of syphon break that can be used are a chamber or portion of the pipework 18 having an increased flow cross-section.

Claims

1. A drainage system comprising pipework and an outlet capable of inducing syphonic flow, the outlet having a tail piece connected to the pipework via a syphon break, whereby the pipework is not subjected to syphonic flow.

2. A system as claimed in claim 1 wherein the tail piece is non-sealingly telescopingly received in an upper end of the pipework.

3. A system as claimed in claim 1 wherein an air inlet is connected to the pipework.

4. A system as claimed in claim I wherein the sypbon break comprises a portion of the pipework having an increased diameter or a chamber having a relatively larger flow cross section.

5. A method of connecting a rainwater outlet capable of syphonic operation to a pipework system, comprising the step of forming a syphon break between the outlet and the pipework system.