Standpipe ops

[RDL210]

Hi,

I have a hydraulics question about standpipe ops. In a building supplied by a standpipe system and a auxiliary pump. This pump assures a 50 psi pressure to the highest outlet and turns on automaticly when water flow is detected.

My question is, when the first out engin gets to this building and supplies the system trough the siamese, is the presure supplied by the engine added to the presure from the aux. pump or is there a check valve that shuts the aux. pump pressure off?

Best regards,

Sly

[FFFRED]

Hi,

I have a hydraulics question about standpipe ops. In a building supplied by a standpipe system and a auxiliary pump. This pump assures a 50 psi pressure to the highest outlet and turns on automaticly when water flow is detected.

My question is, when the first out engin gets to this building and supplies the system trough the siamese, is the presure supplied by the engine added to the presure from the aux. pump or is there a check valve that shuts the aux. pump pressure off?

Best regards,

Sly

Around here to the best of my knowledge there is a check valve that only opens and allows the Engine supply to flow into the riser if it overcomes the pressure of the aux. pump in the building.

FTM-PTB

[HEYVERN]

Hi,

I have a hydraulics question about standpipe ops. In a building supplied by a standpipe system and a auxiliary pump. This pump assures a 50 psi pressure to the highest outlet and turns on automaticly when water flow is detected.

My question is, when the first out engin gets to this building and supplies the system trough the siamese, is the presure supplied by the engine added to the presure from the aux. pump or is there a check valve that shuts the aux. pump pressure off?

Best regards,

Sly

There is also acheck valve after the discharge side of the booster pump. Therefore when the first in engine connects to the FDC, the first engine will supply the standpipe, provided the engine supply pressure is greater than the discharge presure of the booster pump. Also, according to NFPA20, th booster pump should have a manual shut off. It should not automatically shut off.

[RDL210]

There is also acheck valve after the discharge side of the booster pump. Therefore when the first in engine connects to the FDC, the first engine will supply the standpipe, provided the engine supply pressure is greater than the discharge presure of the booster pump. Also, according to NFPA20, th booster pump should have a manual shut off. It should not automatically shut off.

Is there anyway other than pre incident planning (or manual shut off)to know at what pressure the first due should supply the FDC when a booster pump is involved?

If I have a booster pump giving 250 psi to the system and I pump 200 psi from the first in engine thinking I'm overriding the pump, I will, in fact, only add this 200 psi to the 250 psi from the pump and supply the system with 450 psi

Sly

[RDL210]

Around here to the best of my knowledge there is a check valve that only opens and allows the Engine supply to flow into the riser if it overcomes the pressure of the aux. pump in the building.

FTM-PTB

Sorry, I just read your post again and it kind of answered my second question...

It would in fact make a lot of sens if a check valve would only open when engin pressure at the FDC "beats" the booster pump pressure in the system...

Thanks!!! Standpipe ops are not an every day thing around here...

Best regards,

Sly

[HEYVERN]

Is there anyway other than pre incident planning (or manual shut off)to know at what pressure the first due should supply the FDC when a booster pump is involved?

If I have a booster pump giving 250 psi to the system and I pump 200 psi from the first in engine thinking I'm overriding the pump, I will, in fact, only add this 200 psi to the 250 psi from the pump and supply the system with 450 psi

Sly

In our area, we require the sprinkler contractor to post a sign with the stanpipe or automatic sprinkler connections with the system demand information.(ie: GPM @ PSI). And to answer your second question, you are right, the FDC check valve would not open until the pressure was greater than the booster pump. Hope this helps.

[kfactor]

RDL,
Good advice so far, however, the scenario you have is pretty complex hydraulically - not rocket science, but very difficult to predict flows/pressures without a computer simulation.

As I think has been stated, the arrangement you have should be pumps in parallel (the bldg fire pump and the engine connected to the FDC). The FDC piping should tie into the standpipe system downstream of the bldg fire pump. You should verify this - improper installations do happen. With parallel pumps, you add the flows of each pump at the same head/pressure. For example, if one pump produces 500 gpm @ 100 psi and another pump 1000 gpm @100 psi, the combined supply from the 2 pumps operating will be 1500 gpm @ 100 psi. For series pumps, it is just the opposite, add pressures at the same flow (1000 gpm @ 50 psi and 1000 gpm @ 75 psi = 1000 gpm @125 psi).

When the engine pumps the FDC, the hydraulics are pretty complex to estimate estimate without a computer calc. Here's why - the key point in the system is where the FDC piping ties into the standpipe riser. It is only at this point (let's call it point A) where you can determine how much the engine might contribute vs. the bldg fire pump. It is not a simple one or other question. At this point, the pressures have to be same (2 different pressure can't exist at the same point). You may set the engine to pump at say 250 psi, but once you start flowing water, friction loss will kick in and all of the losses of hose and piping between the engine and point A will have to factored in. So lets say your losses are 50 psi flowing 500 gpm. At point A, the engine will produce a flow of 500 gpm and the pressure will be 250-50= 200 psi.

Now you have to look at what the bldg fire pump will do. Most stationary fire pumps are single speed (although newer variable speed drives are avialble). The pump can flow anywhere along its curve, from 0 flow (churn) to theoretically some max flow at 0 psi, but bldg fire pumps (NFPA 20) are cut off at 150% of rated flow (example 1500 gpm for a 1000 gpm rated pump). What the bldg pump will do is move along its curve to match the pressure that the engine is producing at point A. So it will land at a position where the pressure at point A is 200 psi. So let's say that is also 500 gpm, therefore the water supply available at point A is 1000 gpm @ 200 psi (add the flows at same pressure) Where that is on the pumps curve and how much flow that will be is very hard to predict. What happens is that the bldg fire pump will respond to you throttling up at the engine (kind of like magic!). As you throttle up the engine, the pump will move up on its curve - in other words, it will flow less water at higher pressure - as you throttle up, it will in effect "throttle up" and keep producing greater pressure at lower flows. It will do this until it gets to 0 flow and its max pressure (churn). If you can drive the bldg fire pump all the way back on its curve and over come its churn pressure (and flowing the entire demand from the engine), you can completely override the bldg fire pump. And I'm making it a little simple by saying that engine and bldg fire pump will flow 500 gpm. How much you will actually flow will depend on your hose, nozzle and the pressure on that nozzle, etc. Then the flow is balanced by the engine and bldg fire pump. This is all very dynamic, as you change one factor, everything else changes.

Bottom line is that short of flow test or a set of hydraulic calcs, it is almost impossible to predict where things end up. I would say that it will be difficult to completely overcome the bldg fire pump. If you want to get ball park idea of what you need to pump at you can try this - find out what the churn pressure is on the discharge side of the pump. Lets say 200 psi. Now in order to completely override the bldg fire pump, you need to be able to flow the required gpm at a pressure greater than 200 psi at point A (not at your pump panel). In order to do this, you need to be able calculate the losses between the engine and point A. Let's say you want to flow 500 gpm and losses are 50 psi - that means you must pump at 250 psi to completely override the bldg fire pump. A word of caution though, depending on how the bldg fire pump and standpipe was designed and how much losses you have between your engine and point A, you could end pumping at such a high pressure that it is mcuh greater than what you want at the standpipe discharge etc. In that case, you essentially end with the bldg fire pump and the engine sharing the demand.

If you had some actual conditions you could post, we could try to run some calcs and see what it looks like.
Good luck

[HEYVERN]

KFACTOR, I could not of explained it better myself. But one thing that we need to think about is the hydrant that is supplying the engine is usually on the same underground line supplying the building booster pump. Therefore when you trottle up the engine the booster pump may go into low suction.

[kfactor]

Absolutely HEYVERN, excellent point. There are number of factors, details, etc. that I didn't get into (post was getting long!). Suction pressure is a key one as you mention, it's one you have think about a while, but as you throttle up the engine and increase flow through the FDC, that will lower suction pressure to the bldg fire pump, lowering its overall discharge pressure - favoring the engine. And then you have friction loss a function of flow, etc. A key factor I didn't mention is that the bldg pump/standpipe is typically desiged for 500 gpm at the most remote standpipe, 250 gpm for all others. You might have a pump sized for 1000 gpm of standpipe flow. However, in a fire scenario, you might only be using 250-300 gpm worth of that. The bldg fire pump will be flowing 250-300 gpm at a higher pressure than its rated 1000 gpm pressure - this would work against the engine overriding the bldg fire pump. It's a complex set of factors all working dynamically.

[LVFRENG1]

RDL210

We have alot of highrises in my area. Heres how we do it, you need to know what pressure the system pumps itself. To find this info talk to the building Engineer, or look in the pump control room. There should be a log book in there that has this info in it along with last test and maintance done on the pump.

Then make your hook up and charge to 50 psi below that pressure. We don't take over the system in less their system fails. Remember that system was designed to pump it self at the appropriate pressure. Then if their system fails you run your pressure 50 psi above what theirs run that way if their pump tries to kick back in it wont be able to open the clapper valve and effect the pressure your pumping. The PRV's on each floor will maintain the appropriate pressure.

Hope this helps

[HEYVERN]

Absolutely HEYVERN, excellent point. There are number of factors, details, etc. that I didn't get into (post was getting long!). Suction pressure is a key one as you mention, it's one you have think about a while, but as you throttle up the engine and increase flow through the FDC, that will lower suction pressure to the bldg fire pump, lowering its overall discharge pressure - favoring the engine. And then you have friction loss a function of flow, etc. A key factor I didn't mention is that the bldg pump/standpipe is typically desiged for 500 gpm at the most remote standpipe, 250 gpm for all others. You might have a pump sized for 1000 gpm of standpipe flow. However, in a fire scenario, you might only be using 250-300 gpm worth of that. The bldg fire pump will be flowing 250-300 gpm at a higher pressure than its rated 1000 gpm pressure - this would work against the engine overriding the bldg fire pump. It's a complex set of factors all working dynamically.

I agree completely!!

[Dave1983]

Is there anyway other than pre incident planning (or manual shut off)to know at what pressure the first due should supply the FDC when a booster pump is involved?Sly

None that I can think of. Our county SOG is to charge FDCs at 150psi to start. We then let the crews operating the streams tell us if they need more pressure.