NO20150883A1

NO20150883A1 - Safety device for reducing fluid hammer in a fluid piping

Info

Publication number: NO20150883A1
Application number: NO20150883A
Authority: NO
Inventors: Stein Madland
Original assignee: Fire Prot Engineering As
Priority date: 2015-07-07
Filing date: 2015-07-07
Publication date: 2016-03-14

Description

SAFETY DEVICE FOR REDUCING FLUID HAMMER IN A FLUID PIPING

The invention relates to a safety device for reducing fluid hammer in a fluid piping. The invention more particularly relates to a safety device for reducing water hammer in a water piping, such as supply line of a firewater system.

Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change). A water hammer commonly occurs when a valve doses suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It is also called hydraulic shock. This pressure wave can cause major problems, from noise and vibration to pipe collapse. It is possible to reduce the effects of the water hammer pulses with accumulators, expansion tanks, surge tanks, and other features. An application area where water hammer is a severe problem is firefighting using firewater monitors. A firewater monitor is a device used to supress a fire in a fire hazard area. The firewater monitor is typically located away from the area it protects, and can cover the area by a water spray or a water jet from a distance to the fire. Typically, the firewater monitor can be located 20 to 40 meter away from the area it protects. The monitor can be rotated, and the elevation angle of the water discharge can be adjusted up or down. The firewater monitor can be remotely operated by use of hydraulic or electrical remote control, it can be arranged with an oscillating device, which will cause it to oscillate over a preset sector, or it can be purely manually operated. Water pipings in such systems are carrying high-pressure water columns running at very high speeds. The water hammer is caused by the sudden reduction in cross section flow area which the moving water column in the dry section of the piping experiences when reaching the monitor nozzle that has a much smaller cross section area than the feed pipe. Water hammer effects in such systems, for instance when opening the release valve, may easily produce pressure surges over 100 bar, in the final dry pipe section that is connected to the release valve. The longer this dry pipe section, the bigger the water hammer effect, which is the reason that in the prior art, the dry pipe sections (between the last release valve and the monitor) are generally kept short (which is not desired for firefighting as you cannot get close to the fire), or dedicated expensive valve systems very near to the end of the piping are used.

US3,018,799 discloses another safety device for reducing fluid hammer.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments.

In a first aspect the invention relates to a safety device for reducing fluid hammer in a fluid piping for transporting a fluid column in a downstream direction. The safety device comprises a diffuser placed in a centre region of the fluid column in operational use for redirecting fluid from the centre region of the fluid column to the outside. The safety device of the invention the diffuser comprises a funnel for reducing a cross-sectional area of the fluid column in the length direction in operational use.

The effects of the combination of the features of the invention are as follows. In operational use of the safety device within a fluid piping the diffuser in the centre region changes the moving direction of the incoming fluid, which slows down the fluid column before it hits a tap or a firewater monitor, for example, that is mounted downstream of the diffuser at the end of the piping. Calculations have shown that the flow speed can be reduced with 40% to 50% in some embodiments of the invention. Placing the diffuser in the centre region is particularly effective because the flow speed within a fluid piping is typically highest in the centre region. The effective flow cross-sectional area is yet also a little bit reduced, but this gives only a small pressure drop at nominal fluid flow (typically at 5 to 10 bar). The funnel forms an effective device for slowing down the fluid velocity as well as creating a higher pressure at the centre region such that the fluid column is pressed to the outside after passing though the funnel. What is meant with the terms "upstream" and "downstream" is further illustrated in the description of the figures, yet such terms are quite common terms for the person skilled in the art.

In an embodiment of the safety device of the invention the diffuser comprises a conical or bell-shaped body, wherein the conical or bell-shaped body is arranged axially with respect to the fluid piping and wherein a narrow end of the conical or bell-shaped body is directed in the upstream direction. The use of a conical or bell-shaped body in the centre region of the fluid piping håving its narrow end pointed in the upstream direction is a convenient and efficient way of achieving the effect of redirecting fluid from the centre region to the outside or outer region. The funnel is preferably placed upstream of the conical or bell-shaped body and the cross-sectional area reduces in the downstream direction. The funnel placed in front of the bell-shaped body forms an effective device for slowing down the fluid velocity as well as directing the fluid column on the bell-shaped body in that the fluid is more effectively redirected.

In an embodiment of the safety device of the invention the funnel is provided with apertures around its circumference for allowing the fluid to escape from the centre region of the fluid column to the outside. Implementing apertures around the circumference of the funnel contributes to the redirection of the fluid column, in that fluid can escape the inner region of the funnel.

In an embodiment of the safety device of the invention the funnel comprises a series of sub-funnels that are placed axially with regards to each other, and wherein said sub-funnels are placed such that an aperture is formed in between each neighbouring pair of said sub-funnels, wherein said aperture is for allowing the fluid to escape from the centre region of the fluid column to the outside. Implementing apertures between each of sub-funnels in a series of sub-funnels contributes to the redirection of the fluid column, in that fluid can escape the inner region of the funnel. This embodiment may also be combined with the previous embodiment.

In an embodiment of the safety device of the invention the safety device further comprises at least one orifice plate arranged downstream of the diffuser. Orifice plates further contribute to the slowing down of the fluid column.

In an embodiment of the safety device of the invention the safety device is configured to be placed within the fluid piping and fixed to an end portion of the fluid piping. This embodiment is advantageous, because it provides for a space-saving solution. Expressed differently, the safety device is placed within the fluid piping, and thus does not require additional space downstream of the end of the fluid piping.

In an embodiment of the safety device of the invention the safety device is free of movable parts. It is a significant advantage of the invention that the device is a fully passive mechanical structure, i.e. it does not require any movable parts. An embodiment without such movable parts is thus very advantageous.

In an embodiment of the safety device of the invention the safety device is free of reservoirs or expansion chambers. It is a significant advantage of the invention that the device does not require any movable parts. An embodiment without such expansion chambers is thus very advantageous, i.e. space-saving.

In an embodiment of the safety device of the invention the safety device is free of resilient members. It is a significant advantage of the invention that the device is a fully passive mechanical structure, i.e. it does not require any resilient members. An embodiment without such resilient members is thus very advantageous.

Hereinafter follow a couple of application areas of the safety device of the invention. However, the invention is not limited to these application areas. Water hammer or fluid hammer is a problem, which occurs in many different systems.

In a second aspect the invention relates to a water system comprising a water piping håving an end portion for connecting to a tap, wherein the end portion of the water piping is provided with a safety device according to the invention. This embodiment forms a first application area of the invention.

In a third aspect the invention relates to a firewater system comprising a firewater piping håving an end portion for connecting to a firewater monitor, wherein the end portion of the firewater piping is provided with a safety device according to the invention. This embodiment forms a second application area of the invention.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein: Fig. 1 shows a water piping system håving a safety device in accordance with a first embodiment of the invention; Fig. 2 shows the safety device of Fig. 1; Fig. 3 illustrates a main principle behind the invention; Fig. 4 illustrates a specific part of the safety device of Fig. 1 in more detail; Fig. 5 illustrates another safety device in accordance with a second embodiment

the invention, and

Fig. 6 illustrates the water flow in the embodiment of Fig. 5.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Throughout the Figures, similar or corresponding features are indicated by same reference numerals or labels.

In the embodiments described hereinafter there is a strong focus on firewater systems. However, the invention is not limited to such systems at all. The invention may be applied to any fluid system. Thus, at all places where the word "water" is used this may be replaced with "fluid", including any liquid or gas, or mixtures thereof. Fig. 1 shows a water piping system 1 håving a safety device in accordance with a first embodiment of the invention. The water piping system 1 in this example is a firewater monitor system, which comprises a so-called monitor 200 that is mounted on a water piping 900. The figure also shows a safety device 100 in accordance with the invention, which is mounted within the water piping 900. Fig. 2 shows the safety device 100 of Fig. 1. The safety device 100 comprises a set of support ribs 10 (in this embodiment 4) which at least serves as mechanical frame together with the parts that are mounted thereon. Other mechanical frame constructions are also possible. At an upstream side 900u of the safety device 100 there is provided a diffuser 50. In this embodiment the diffuser 50 comprises a funnel 53, which is put in series with and upstream 900u of a conical or bell-shaped body 52. In this embodiment the funnel 53 comprises three sub-funnels 54,56,58 placed in series and spaced apart from each other. The diameter of the middle sub-funnel 56 at its widest side is substantially equal to the diameter its predecessor 54. The diameter at the narrowest side of each the middle sub-funnel 56 is substantially equal to the diameter of its successor 58. Downstream 900d of the diffuser 50 there is placed an orifice plate 60, which further slows down the water flow. Fig. 2 further shows a coupling flange 70, which serves to couple the safety device 100 to an end of the water piping (not shown) and to be coupled to a monitor (not shown). The coupling flange 70 may be designed to match with the dimension of the firewater monitor to be used. The dimen-sjon of the support ribs 10 and diffuser elements is to be matched with the dimension

of the water piping within which it is to be used. In case the invention is applied in a firewater monitor the dimensions can be made to fit to various pipe flange dimensions

(three inch, four inch, six inch, eight inch, ten inch or twelve inch.)

The safety device 100 may additionally be provided with a dump valve 80, but this is purely an option. Dump valves are typically used to provide a certain reduction of the remaining pressure shock. Such valves are typically fully open in a standby situation, and they close automatically after a predefined time interval with help of water pressure when the firewater monitor is pressurized.

The main purpose of the diffuser 50 is to change the direction of the water current such that water from a centre region of the water piping is redirected to the outside. This will be explained with reference to Fig. 3, which illustrates a main principle behind the invention. The figure shows an enlarged view of the diffuser comprising the conical or bell-shaped body 52 and the series of sub-funnels 54,56,58 as previously discussed. Also illustrated are the apertures 55,57 between the sub-funnels 54,56,58. The water flow is illustrated by means of the dashed arrows. All elements of the diffuser 50 contribute to a redirection of the water from a centre region 920 to the outside, wherein "outside" is to be understood as the outer regions 922 of the cross-sectional area of the water piping as illustrated in Fig. 3. As far as the funnel is concerned this effect is achieved by providing said apertures 55,57 between the sub-funnels 54,56,58. In an alternative embodiment the sub-funnels 54,56,58 could be provided with holes for letting out the water. In yet an alternative embodiment one large funnel håving such holes is used instead of three sub-funnels. Fig. 3 also illustrates more clearly that a narrow end 52-1 of the conical or bell-shaped body is directed to the upstream direction 900u.

Fig. 4 illustrates a specific part of the safety device 100 of Fig. 1 in more detail. This figure serves to illustrate the orifice plate 60 in more detail. The orifice plate 60 comprises a plurality of holes 61 that are distributed equally over the surface. Orifice plates as such are well-known components, yet they do contribute to a slowing down of the water speed.

The embodiment of the safety device 100 as illustrated with reference to Figs. 1 to 4 works as follows (in a firewater monitor). When the water starts to move in dry section of the water piping it will hit the safety device 100 at high speed (several meters per second). When the water hits the safety device 100 it will meet the three sub-funnels in quick succession. The cross-section area in the length direction reduces strongly over these sub-funnels 54,56,58 and the water will be pressed out through the apertures 55,57. After that the remaining part of the water has passed through the third sub-funnel 58 it will hit the conical or bell-shaped body 52, which presses this remaining water also to the outside. From where the flow speed in the centre region 920 was the highest before the water column hit the safety device 100, have we now reached the situation that the water in the centre region 920 has been completely stopped and forced to the outside region 922. After the diffuser 50 the water will meet the orifice plate 60 (but this element is fully optional), which will further slow down the water flow speed.

Preferably, the sum of the areas of the apertures 54,56,58 including the aperture 58 between the third sub-funnel and the conical or bell-shaped body 52 is adapted to correspond with the flow area of the firewater monitor 200. The same applies for the sum of the areas of the holes 61 in the orifice plate 60, which is preferably also equal to the flow area of the firewater monitor 200.

Fig. 5 illustrates an other safety device 100' in accordance with a second embodiment

the invention. In this embodiment there is an extra orifice plate 65 placed downstream of the first orifice plate 60. Fig. 6 illustrates the water flow in the embodiment of Fig. 5 by means of the fat arrow lines. It is clearly illustrated how the water is forced to flow from the centre region to the outside regions similar to the embodiment of Figs. 1 to 4, i.e. the water speed profile of the water column is significantly changed in that the speed at the centre region is no longer higher than at the outside region. Each of the elements will create an additional reduction in flow velocity.

The safety device as described with reference to the figures may be installed on a

firewater monitor or other firewater piping. The safety device reduces the water hammer, which arises when the empty piping is filled with water. The cross-sectional area of the flow reduces with 80-90% when the water hits the nozzle of the firewater monitor. The pressure shock at the nozzle may easily reach up to 100 Bar, which may even completely tear off the nozzle or the final part of the piping. For this reason firewater monitors are typically rarely used today.

When firewater monitors are used, are they conventionally mounted mainly directly on an automatic release valve such that the dry section of the water piping (the part between the valve and the nozzle/monitor) remains short. That means that conventionally there is a need for one release valve per firewater monitor, which is a relatively expensive solution. Alternatively, the systems must be designed with a very short dry section of the water piping, which means that the nozzle cannot be far away from the release valve, while it is desired that the release valve is located as far as possible from the hazardous places.

This is exactly where the invention provides a solution, because the invention makes it possible to either design the dry section of the water piping longer, or it is now possible to share the expensive automatic release valve amongst multiple firewater monitors.

The invention provides for a simple mechanical unit that can be installed in existing or new water systems, and will give an effective hydraulic damping of the water speed when the water passes through the water piping. This will contribute to an effective reduction of the pressure wave in the water system, such as a firewater monitor. The safety device is very easy to install, and does not require any modification of the piping configuration, and will only result in a small nominal pressure drop in the nominal flow. Therefore, in case of use on a fire extinguishing system, the extinguish properties will not be changed.

Claims

1. Safety device (100, 100') for reducing fluid hammer in a fluid piping (900) for transporting a fluid column in a downstream direction (900d), wherein the safety device (100, 100') comprises a diffuser (50) placed in a centre region (920) of the fluid column in operational use for redirecting fluid from the centre region (920) of the fluid column to the outside (922),characterised in thatthe diffuser (50) further comprises a funnel (53) for reducing a cross-sectional area of the fluid column in the length direction in operational use.

2. The safety device (100, 100') according to claim 1,characterised in thatthe diffuser (50) comprises a conical or bell-shaped body (52), wherein the conical or bell-shaped body (52) is arranged axially with respect to the fluid piping (900) and wherein a narrow end (52-1) of the conical or bell-shaped body (52) is directed in the upstream direction (900u).

3. The safety device (100, 100') according to claim 1,characterised in thatthe funnel (53) is provided with apertures around its circumference for allowing the fluid to escape from the centre region (920) of the fluid column to the outside (922).

4. The safety device (100, 100') according to claim lor3,characterised in thatthe funnel (53) comprises a series of sub-funnels (54, 56, 57) that are placed axially with regards to each other, and wherein said sub-funnels (54, 56, 58) are placed such that an aperture (55, 57) is formed in between each neighbouring pair of said sub-funnels (54, 56, 58), wherein said aperture (55, 57) is for allowing the fluid to escape from the centre region (920) of the fluid column to the outside (922).

5. The safety device (100, 100') according to any one of the preceding claims,characterised in thatthe safety device (100, 100') further comprises at least one orifice plate (60, 65) arrange downstream of the diffuser (50).

6. The safety device (100, 100') according to any one of the preceding claims,characterised in thatthe safety device (100, 100') is configured to be placed within the fluid piping (900) and fixed to an end portion of the fluid piping (900).

7. The safety device (100, 100') according to any one of the preceding claims,characterised in thatthe safety device (100, 100') is free of movable parts.

8. The safety device (100, 100') according to any one of the preceding claims,characterised in thatthe safety device (100, 100') is free of reservoirs or expansion chambers.

9. The safety device (100, 100') according to any one of the preceding claims,characterised in thatthe safety device (100, 100') is free of resilient members.

10. Water system (1) comprising a water piping (900) håving an end portion for connecting to a tap, wherein the end portion of the water piping (900) is provided with a safety device (100, 100') according to any one of the preceding claims.

11. Firewater system (1) comprising a firewater piping (900) håving an end portion for connecting to a firewater monitor (200), wherein the end portion of the firewater piping (900) is provided with a safety device (100, 100') according to any one of claims 1 to 9.