What if any are the pros and cons of placing a pump on hydrant when using LDH?
What if any are the pros and cons of placing a pump on hydrant when using LDH?
Whether you need to or not really depends on the quality of the hydrant and how long the lay-out is. Really hard to know pros and cons without knowing some details, but here goes:
Pros: engine available to boost pressure for a long lay.
cons: engine may block other incoming apparatus
If the hydrant can't supply the water, it can't supply the water. pumping LDH MAY have minimal benefit depending on the situation.
An engine is tied up at the hydrant, that depending on the situation may be more useful elsewhere.
From this it looks like the cons outway the benefits, but if it's a long lay and you need the water put the engine on the hydrant.
Engine on the hydrant - feeding L.D.H.
The higher the hydrant pressure and the larger the main, the less likely the engine will be needed on the hydrant. (We have some locations with 180 psi on 20" mains) Conversely, the lower the head pressure (closer to the reservoir elevation) and the higher the demand for water (master stream application) the more likely it will be that an engine will be needed on the hydrant. Additionally, the longer the lay, the more likely you will need to push the water from the hydrant to the fireground. Having said the above, here is how we address these problems. First due engine goes directly to the scene and pulls attack lines. All 4 engines are similar set-ups with 4 or 5 - 1 3/4" - 200 ft attack lines with TFT's. SOP is for 180 psi PDP or about 180 gpm per line (900 gpm) Also have 2 - 2 1/2" P.C.'s at 250 gpm or total application rate of 1400 gpm. This application rate ramps up with time and arriving firefighters. Second due engine lays out to the hydrant - water supply. Max hydrant spacing is 1,000 ft, so charging the supply line is done strictly with hydrant pressure with the supply pumper connected and left out of gear. Water usage (2-1 3/4 & 1- 2 1/2) or 610 gpm has about 2.5 psi per hundred for 5" hose, therefore any hydrant capable of 30 psi at 600 gpm will be adequate to supply the needed flow. Expanding the handlines to 1220 gpm will cause the Fl to rise 4X to about 10 psi per hundred. Supply PDP needs to be raised to 120 psi. That is 100 psi friction loss plus 20 psi incoming at the attack engine. Pulling back to an exterior position and placing a master stream device (2" SS tip) in operation as well as both 2 1/2's will get you to about 1500 gpm. This causes about 150 psi friction loss plus 30 psi incoming at the attack engine or 180 pdp on the supply engine. This is max for 5" LDH so you are flat out. This arrangement requires at least a 2000 gpm rated pump at the hydrant. (70 % at 200 psi = 1400 gpm) The attack engine will be running around 170 pdp, but has an incoming of around 30 psi. This is a net PDP of 140, so it can be a 1500 gpm pump. Hope this gets you thinking. If you want the flexibility to cut the supply engine into or out of the system, buy a Mushaw or hydrant assist valve and have the first engine lay in and assign a supply engine only if you need the extra water.
As long as the size of LDH is at least the size of the water main, I dont see the need in placing a truck at the hydrant. By using the LDH you are essentialy extending the water main. The system itself should be able to supply it fine.
We do not generally boost LDH, however we have a few spots involving steep uphill lays where the engine on the hydrant makes a big difference. One spot in particular has only 30psi static at the top of the hill during low consumption periods (drops to 20 during peak consumption). In that spot a relay from the bottom of the hill through 1000' of 4" boosts to an easy 80psi or better.
To circumvent the issue of tying up the engine, we use a humat on these particular scenarios so the boost engine can always leave if needed without completely interrupting the supply. Also allows us to demobilize that piece earlier once overhaul is well underway.
Access is not an issue for us.
We have one section of "our fair city" that has low water pressure and requires an engine on the hydrant.
This is a case where a hydrant assist valve would be usefull. First engine stops at the hydrant attaches the valve and lays hose to the fire. After the hydrant is opened if there is sufficent pressure, then you are all set, if not, an engine can go to the hydrant and hook up to the assist valve and increase the pressure to the attack engine without ever breaking the flow to it.
I might suggest that anyone in this series of posts that doesn't think positioning an engine on a hydrant, using the largest diameter and shortest length piece of hose to connect it, can't make a difference in available water supply, spend some time actually doing it. For starters take an engine and position it at the hydrant and supply a truck, flowing a 2" tip, 400' away. Account for a way of measuring tipp pressure so you can discern flow. Move the same engine, on the same hydrant, and have it supplied from the hydrant 200' away and pump the water 200' to the same truck. Finally take the engine and supply it with the 400' of large diameter hose from the hydrant and pump the water 50' into the truck with the same tip. Available water supply is measured by residual pressure, once a flow starts. Watch what happens to the intake guage each time. What you will find, depending on the arrangement you chose, the mere fact of the way you arrange and set up can make an excellent hydrant, one that is capable of supplying thousands of gallons of water, and turn it into a fraction of its capability. Anyone who thinks that it doesn't make a difference where the engine is, in relationship to the hydrant, has had the training service fail them. Now, do I think that every fire that we go to needs to be hedged so that a maximum flow can be developed? No. But in the day and age of 2000 gpm pumpers, that I would venture to say have never been utilized to their capacity, where you position an engine has a direct relationship on your ability to use it, if the water is in the ground. Aside from the water issue there is a myriad of other reason why the apparatus belongs as close to the hydrant as possible.
That being said, we most often opt for the attack engine to start off tank water and the second due reverse lays to the hydrant.
2nd due brings in the line. Hydrant guy makes the hydrant, installing the hyd assist valve + a 2 1/2" gated valve. SOG is to install the HAV whether laying fire to water or water to fire.
Going from 2, 3 inch lines to the hydrant to LDH was the best change ever in suppling the pumping Engine in my mind. No real cons in using LDH at least not in my response area.
This is amusing and funny at best. Everyone is only thinking about using LDH with a hydrant.
How about this. You drop the suction from your truck in a pond and relay pump to the scene? LDH allows for greater water flow at a lower pressure. You can also get large amounts of water over a greater distance. Using this method you can easily get 1500 GPM a mile away.
LDH is nothing more than a portable water main. We used to run two or three 3 inch lines between trucks, now we run a single 4 inch line. The hose isn't that heavy and it is easy to pick up.
The downside comes in mutual aid situations where the mutual aid departmetns aren't set up the same as you are.
Depends on the GPM available from the hydrant, how much of that you need, how long the lay is, what size hose, and what the FL of your hose is. Our SOP is to reverse lay and drop both the bundles and the LDH in front of the scene before proceeding to the hydrant. We use 4", and we pump the hydrant or put in a relay pumper if the lay is over 400'. Otherwise the FL will prevent us from pushing enough water through to use more than 2 lines.
For example: our usual hydrant pressure is 70-80 psi, flowing about 1000 gpm. FL for 1000gpm in our 4" is almost 20psi/100'. Without a pumper to boost the pressure, the FL will drop your flow significantly at 400'.
The predominant issue with the hydrant is the pressure at which it delivers the flow, not the GPM. A hydrant that delivers 1500 GPM at 20 PSI (residual) will get less water to you versus a hydrant that delivers the same flow at 60 PSI (residual).
Hooking a supply line to a hydrant and laying hose without an engine on it is basically the same principle as hooking an attack line to the hydrant. You lose control of the ability to regulate its flow to overcome friction loss as the demand for water increases.
Sometimes it is misunderstood, but think of residual pressure on a hydrant as its pump discharge pressure. Think of the hydrant as a pump. Friction loss for 1500 GPM in 5" hose is somewhere around 15 PSI per 100'. With no engine on the first hydrant (flowing at 20 PSI residual), youd only move that 1500 GPM about 150'. Adding an engine allows you to move that flow substantially farther or to move a greater amount of water over less distance.
A hydrant open fully delivers its capacity at almost no pressure on most water systems. So, by attaching a short section of 5" or 6" intake hose to the pump, you can get that water into the pump and add pressure to it to push it down the line to the scene. Remember, the pump is adding energy to the water (we see that as pressure) its not making water.
Using the second example (60 PSI residual) you can move 1500 GPM about 400 feet if no engine is at the hydrant.
You can assume that most of the time you'll have the water you need or you can plan for a fire to escalate and have an engine on the hydrant. If it isnt necessary, the hydrant engine can simply leave its pump disengaged and allow the water to flow through to the engine at the scene.
The size and length of intake hose you use n the hydrant (when using an engine on the hydrant) will also affect the residual pressure reading of the hydrant. For example, one day using a 5" front suction line (25') I got 1035 GPM at 40 PSI residual and then 920 GPM at 20 PSI residual when I switched to a single 3" 25' long to the aux intake. Use the largest and shortest hose to connect directly to the pump from the largest hydrant connection whenever possible for MAXIMUM water. Using smaller, longer hose or going through aux suctions or front intakes will affect the maximum available water.
Ultimately, knowing your water system will fill in some of the blanks.
A 1500 GPM pump at draft moves the water at about 150 PSI (give or take a few PSI). The FL of 1500 GPM is 15 PSI per 100' in 5" hose. That draft engine can only move 1500 GPM a little over 850 feet if the receiving engine is maintaining a 20 PSI residual intake reading.
Also have to account that most pumps over 1500 GPM require dual suction lines from main pump suction inlets. If you only have one line in the water and especially if its off the front suction, cut the total discharge capacity substantially.
For reference, FL in 5" hose (theoretical) is losted below for GPM (left column) and FL per 100' of hose in right column.
Contrary to popular belief, friction loss does occur between the hydrant and the attack pumper. Next time you train put a gauge on one of the 2 1/2" outlets and see the pressure difference between the hydrant and the intake on your pump. You will be amazed at the pressure drop when flowing the maximum amount of water with the set-up that you are working with.
I would recommend if you need big-water pump the hydrant. Another recommendation is to stretch 2 five inch supply lines from the hydrant to the supply pumper. This allows more water to flow into the pump at basically the same hydrant pressure.