IEEE Article

 

 Re-supplying Water after an Earthquake


      Relay Pumping  via a Digital Network for First Responders
 

Steve Shoap, Life Member IEEE

 IFFC LLC

 Wakefield Massachusetts, USA

 steve.shoap@alum.mit.edu


 Michael Laskaris-PE, Director of Engineering

Fire Suppression Division, Hale Products

 Okala FL, USA

 mlengr@aol.com 



The following paper was published in the proceedings of the 2012 IEEE International Conference on Technologies for Homeland Security

13-15 November 2012, Westin Hotel, Waltham MA

                     

Abstract - Earthquakes often break the water mains in affected localities. The broken mains remove an important source of water for firefighters and the public. Firefighters sometimes use a series of pumper trucks to move water long distances through hoses. In a system with manual control, 

if an operator leaves the pump, the relay will probably fail. Because it is operationally challenging, relay pumping is not used as often as it might be. A solution can be found in a wire based Ethernet network controlling the pumps. 

Such a system using the proposed network will work even if the operator leaves the site. This digitally controlled relay pumping system can be used to supply water to first responders, and civilians. It can be used as an infrastructure restoration strategy. It is also useful in delivering water to fight fires in water deficient areas. 


INTRODUCTION


Relay pumping can supply water over long distances. It uses multiple pumps to overcome the friction losses in a long hose lay. It can supply water for fighting wildfires and also supply emergency water to populations after an earthquake or other disaster destroys water mains. It can even supply cooling water for atomic power plant operations when situations like the recent Fukushima Powerplant Disaster occur.


Existing relay pumping techniques requires continuous manual control of pressures and flows at each booster pump. An operator must be dedicated to each pump and must be able to communicate with all of the other operators on the relay to ensure that pump pressure and flow changes are coordinated. 


In many situations, crews on a relay may be forced to remain at a location that might become dangerous. Terrain may inhibit radio communications. If only one crew leaves a pump, uncontrolled pressures can damage the pumps and hoses, and the relay may fail. 


Adding a digital data network to a relay system changes this scenario dramatically. The data network runs on a wire pair embedded in the hose, and it enables a single operator to monitor and control all of the pumps. The number of personnel dedicated to operating the relay is significantly reduced.  Problems caused by radio communication failures are eliminated, and more personnel are available to actually

deal with the disaster situation. Safety is dramatically improved. In fact, if radio communication fails, the data network can provide an alternate first responder communication path between all pump vehicles. 



DIGITAL NETWORK VS. RADIO NETWORKS

A digital, Ethernet network is similar to a group of pump operators on a common radio frequency. In a traditional relay pumping system, the pump operators use radios to coordinate pump settings. A digital network communicating over a wire pair in the hoses has advantages over a radio network.

Channel Access

In many radio networks, a firefighter waits until the radio channel is not being used and then does a Push to Talk (PTT), and starts talking. If another firefighter does a PTT at the same time, their transmissions will interfere with each other, and valuable time can be wasted.

In the proposed Digital Network, a pump circuit board waits until the wire pair is not being used, and then starts to send a digital message. If another circuit board sends a message at the same time, they both immediately stop sending. Each board waits a random amount of time, and if the wire pair is not being used, it tries to resend the message. If no other circuit board tries to use the wire pair, the message will be fully transmitted. This happens very quickly. In a 10 km relay pumping system with 1 km between pumps, the message delay from the beginning to the end of the system would be less than 1/10 second.

 A relay pumping system may run up hills and go down the other sides of the hills. Pumps behind hills may not be in the “line of sight” and may not receive the radio signals. If some pumps do not get the message to turn on or off, the system hoses and pumps may be damaged.  

  The proposed Digital Network uses a wire pair embedded in the hoses to support the network. It does not need “line of sight” for radio reception. At each pump location, the digital network uses a repeater which allows for networks of virtually unlimited length.  

  Message Integrity   In a radio system, speech clarity may be impaired and the pump setting commands may not be understood.  The radios may not provide a noise free channel. Messages may have to be re-transmitted several times to insure accuracy.   

  If the relay system needs to increase total flow, it is critical that all pump operators acknowledge that the message has been received and act in a coordinated manner. This can be difficult when a large number of pumps are being used. A very rigid protocol of pump operator responses must be enforced. The process might be time consuming and error prone.  

  With the proposed Digital Network, the individual messages in a digital network have a very high accuracy. They are sent as a packet that has error detection and correction mechanisms. If a message is received that is uncorrectable, a retry request is sent to the originator of the message. This all happens in fractions of a second.  

  If a message is sent to a pump, the pump must acknowledge the receipt of the message. Again, this is done in fractions of a second. If the sender does not get an acknowledgement, the sender will resend the message and wait for an acknowledgement.  

These digital network protocols have been refined over the past 30 years, and are very robust. 

 

 WATER HAMMER

  

The emergency water supply systems, by definition, will have various hose lengths, elevations, and distribution arrangements.  An integrated control system that allows various pumping modules to communicate with each other and provide a single or multiple points of control must deal with the phenomenon of water hammer.      The standard most referenced for the specification of mobile water supply systems is NFPA 1901.  This is the same standard that applies to the construction of fire trucks.  Since the application of a fire truck relaying water for fire suppression is very similar to the application of moving water for disaster support, this seems quite appropriate.  In each case, the ability to move water from various sources over varying distances and elevations is required.  NFPA 1901 reminds us in chapter A.16.10.14 that ‘pressure control systems may not respond fast enough to prevent water hammer'.  

  If the prevailing standard and engineering knowledge tell us that existing pressure control systems may not stop water hammer, then how do we protect against water hammer and its damaging effects.  We know that water hammer can damage hose and piping systems.  Water hammer generally comes from the rapid operation of valves.  The momentum or energy in the water has no place to go when a valve is rapidly closed.  A pressure wave can be created that travels at the speed of sound in water, or roughly 4800 feet per second.  That is almost a mile in a second.  It is easy to see how water hammer might be too fast for pressure control systems to react.  Accumulators or surge control devices can be used to absorb much of the pressure surge, but these become impractical for an emergency portable system due to the large sizes required.  Relief valves and pressure governors are not designed to overcome the effect of water hammer, but deal with pressure rise or surges.  

  Fire service and emergency water distribution systems can be prone to water hammer as some of the engineering design controls are not available or practical in a temporary system.  For instance, using larger hose and pipe sizes to reduce the velocity of the water in the hose and thus its momentum is not practical beyond a certain point.  Flows required are changing and determined by the evolving incident, not by a systems engineer’s calculations.  Elevation changes are determined by the environment and a temporary pumping station at the bottom of a hill needs to provide the pressures and flows required thru the hose sizes available.    

  In fact, it is well known that the best way to stop water hammer is to prevent it from ever starting.  This is where the remote control of pumping units and their valves can be a critical key to a safe and efficient water distribution system.  We stop water hammer by making our changes to flows slowly.  Electric valves controlled over a remote network can help prevent water hammer. Even the operating pressures of each individual station can be tailored to maximize the factor of safety for the hose and equipment by coordinating the pressures in the relay. 

The Figure below shows a map of many fires in the San Diego area. On the figure, a 10 mile circle is drawn around each large source of fresh water. (The overlapping circle lines have  been removed.) The area covered by each circle could have  been supplied with water from a 10 mile long relay pumping system. (The elevation changes of the terrain were not  considered here. A longer hose lay to accommodate the elevation variations would not be a problem.)     

The figure suggests that a long, but practical, relay pumping system can supply water to large areas in semi-arid locations. (The map was designed by Anna Casson, Dept. of Geography, San Diego State University).

 SYSTEM FAILURE COMPENSATION  

  The emergency relay pumping system has to function in an arduous environment.  Failures have to be expected.  One of the reasons why Fire Departments all over the world changed from positive displacement pumps to centrifugal pumps is because centrifugal pumps can be ‘pumped through’.  This means that a pump that has run out of fuel or experienced any number of failures can still act as a manifold and water can flow through the pump with minimal restrictions as long as the pump case has maintained its integrity.    

  The system operator needs to know about the failure so other pumps in the system can make up for the loss of the relay station or a repair / replacement can be implemented.  The integrated relay with digital network control allows the operator to see the contribution of each pump and when one drops off line he can take the appropriate action with minimal delay. Alarms can even be easily set so the operator of the network can be alerted to changes in operating conditions.  

The flow rates of a digitally controlled pump relay are limited only by the size of pumps and hoses available.  The digital single station control can make operations safer and more reliable and allow the Water Supply Officer to maximize the output from the equipment and environment.  Water flows in typical fire hose are well established and  without going to extra large specialty hoses, significant flows are available.  Larger pumps and hoses can obviously deliver more water, but one of the points of the equipment discussed here is that it is multipurpose so it can be used for a variety of situations. Standardized hose sizes becomes a consideration for interoperability.  

  Assume a 5 inch hose that needs to deliver 750 GPM in an emergency situation. Its Loss per 100 feet is 4 psi. This translates to 26.4 psi per 200 meters. A one kilometer hose lay will be 5 lengths of 200 meters, so the Pressure Loss will be 132 psi. The inlet of the next pump requires an additional 40 psi. A diesel pump can easily deliver 132 + 40 psi at 750 GPM over the 1 km of 5 inch hose.

  

TECHNICAL FEASIBILITY OF A DIGITAL NETWORK INTERFACE TO DIESEL PUMPS  

  Hale Pumps, one of the larger pump suppliers to first responders, currently controls their large diesel pumps via an SAE J1939 [2] local data network. This network is similar to the Onboard-Diagnostic-Bus (OBD) that is used for engine control on passenger vehicles. The bus reduces the number of wire bundles that are needed for the interconnection of the many sensors and actuators required in a modern vehicle.  

  The SAE J1939 network can easily be interfaced to the proposed Ethernet-type hose based network. Such an interface would provide the ability to monitor and control all of the pumps in a relay system. The data network requires only very low voltage signals on the wires embedded in the hoses and couplers. There is no electrical shock hazard. A simple laptop or industrial computer interface would provide the ability to monitor and control all of the pumps in a relay system.


FEASIBILITY OF EMBEDDING A WIRE PAIR IN A HOSE

The Figure below shows a hose that is already produced by All American Hose (Snap-Tite). The hose contains a single embedded wire that is used to discharge static electricity when the hose is used to deliver diesel fuel to remote military posts. The hose is already qualified to deliver potable water.

All American Hose has indicated they can replace the single embedded wire with an embedded wire pair that will support the digital network.

  

The data network circuit board assemblies are proven technology and can be integrated into the diesel pump electronics at a reasonable cost. A typical 1000 GPM trailer or pump module might see a 2-5% increase in cost to be equipped with the remote digital network control which can be accessed with a rugged laptop. The cost of a second wire added to a hose will also be modest. Any pumping unit equipped with remote digital network control can still have manual controls to run locally, so a unit equipped with this option has full flexibility to run in a variety of situations with or without a network.


CONCLUSION

Using a digital network embedded in fire hose creates a powerful control system that not only provides remote control and improved manpower availability, it can add to safe operations because of a more reliable view of the system. It can also keep First Responders out of hazardous areas. The system cost increase is minor, and the improvements in capability are significant.

REFERENCES

[1] http://www.iridium.com/DownloadAttachment.aspx?attachmentID=1408

[2] http://www.sae.org/standardsdev/groundvehicle/j1939a.