When it is necessary and compulsory to use a pilot valve in a Diesel fire equipment installation?
NFPA 20 requires a pressure-relief valve in the discharge piping where a total of 121% of the net rated shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation, exceeds the pressure for which the system components are rated.
You can use pilot or adjustable spring-loaded mechanism.
Michal, thank you for your response. This means that when the 300psi is not exceeded, the standard does not require the piloted valve ?.
If you have sprinklers, then your system is rated to 175psi. If 175 psi is not exceeded ([121% shut off pressure - ex. 130 psi + suction - that is usualy at -10 psi (it's minus but you need to add it)] x 1.21 = 169 psi) then piloted valve is not required.
If your weakest component is rated at higher pressure then you compare it to the higher pressure than 175psi.
Reference to this is in NFPA 20 (18.104.22.168).
The standard specifically does not permit the use of a main pressure relief valve on an electric fire pump, except where a variable speed driver is used. Variable speed drivers are required to default to constant rated speed operation. In the event the variable speed driver fails, the rated speed can result in system over-pressurization. In this case a pressure relief valve is required.
When designing a fire pump, it is highly important that the designer match the pump to the system demands, in order to avoid overpressurizing the system and then using pressure regulating devices to compensate.
Thanks for your answer. You have made this very clear to me.I only have one doubt as to the choice of the piloted valve.
Case 1: Fire pump outlet pressure: 280 psi Closing pressure: 323 psi. Maximum pressure of 300psi accessories. What type of pilot valve should have: a 175psi, or 300psi or more than 300psi support.
Case 2: Fire pump outlet pressure: 155psi Closing pressure: 178 psi.Maximum pressure of accessories weaker 175psi. What type of pilot valve to use: a 175 psi or we should use one that supports 300psi.
The choice of the piloted valve must be according to the discharge pressure of the equipment or must the pressure of the equipment shutdown also be taken into account?That is, for discharge pressures of less than 175psi, use pilot valves of 175psi and for discharge pressures greater than 175-300psi use pilot valves at 300psi, or take into account the closing pressure for their selection.
Thank you ,
I assume that you have 2 separate circuits.
If not please just let me know
Case 1: Closing pressure 323 psi + static suction 10 psi x 121% = 403 psi - acc to NFPA your weakest components should be rated above 403 psi to avoid pilot valve - 300 psi pilot required
in this case closing pressure 323 psi is already more than your accessories are rated - yes you need pilot without above calculation.
Case 2: Closing pressure 178 + static suction 10 psi (I assume the same water tank) x 121% = 227.48 psi - 175 psi separate pilot required
The choice of the piloted valve must be according to max. operating pressure of the equipment - for sprinklers it will be 175 psi, for valves only in some transit piping it will be 230 or 300 or 360 psi.
Always choose pilot valves to protect the weakest link in your installation. Your pilot will be rated at the maximum allowable working pressure of your weakest accessories. For sprinklers it's 175 psi that is indicated in data sheets, for other components it will be just protection against damage - piping, couplings, valves, fittings. If you have sprinklers installed, your pilot valve must be at max. working pressure of your sprinklers that is 175 psi.
Then I must always consider the closing pressure of the fire pump and not the nominal pressure, for the choice of the capacity of the piloted valve. That is, if I have a sprinkler system and the closing pressure is greater than 300 psi, I will need to choose a pilot valve that will withstand the 300 psi and protect the 175psi accessories?
My question is focused on the choice of the capacity of the piloted valve, when it should be 300 psi or 175psi or more than 300psi. For this I only have to look at the closing pressure or the nominal pressure of the pump?michal.lein
Closing pressure tells you if you need it.
Accessories tell you what opening pressure of pilot valve
Louis, to answear what pressure you need, I need to see some scheme first.
I assume that you have 2 separate circuits. But from what you say, both pumps are connected to one installation?
Michal,The equipment has not been installed yet. I am making this query because I need to buy the pilot valve for the equipment that we must install. Then there are two teams for two different projects. The piloted valves come to support some 175psi and others at 300psi and there are some for more than 300psi. Then I need to choose which one to use.
What systems do you have there. Are there 3?
I do not have that information. They only supply us with the data of the equipment and since you know that the valve is an accessory, we must choose the appropriate type of valve according to the parameters of the equipment that they buy from us. That's why I had the question, thanks to your information, when the valve should go. Now when we have to buy the valve these come from 300psi and 175 psi, should we select according to the output pressure of the equipment? or to the closing pressure of the equipment?
That is: 750GPM 160PSI Closing pressure 180 psi.We determine that it requires a pilot valve.Which valve do you buy? The one that supports 175 PSI 150 # or the one that supports 300PSI 250 #?
In this case 175 PSI, definitely.
Your pump is relatively small. Size of your valve is 4''(in)/6''(discharge)
Table 5.25(b) NFPA 20
I have been very helpful with your response. I'm just consulting about these two cases:
1. 750GPM 250PSI Pressure shutoff: 318 PSI. Which valve to buy: Class 150: avaliable 0-200psi Class 300: avaliable 100-300psi or should be a higher pressure.
2. 750GPM 270PSI Pressure shutoff: 328psi. Which valve to buy: Class 150: avaliable 0-200psi Class 300: avaliable 100-300psi or should be a higher pressure. 100-730 psi.
Another very important question is at what pressure should I set the pilot valve: shutoff pressure or nominal pressure.
Thank you so much.
If we talk about this pump only: 750GPM 160PSI nominal pressure and 180 psi shutoff pressure.
then you need to protect sprinklers only - and you need 175 PSI Cla-Val Class 150: 0-200psi.
no other relief required.
is there any other pump you didnt tell me?
You mentioned something about fire pump: outlet pressure: 280 psi closing pressure: 323 psi.
Is it another pump?
Yeah that's right. It is another bomb. That's where I have my doubt, which valve should go, if cla-val goes up to 300psi. There is another brand that goes up to 700psi but it is not listed. What should we do here?
We also have another 750GPM 270PSI Shutoff pressure equipment: 328psi. We plan to install the 300-psi Cla-Val valve, thinking about setting it to 280 psi, and that it does not reach 300psi so as not to affect its use as it goes up to 300psi, this thought is correct ?.
It makes sense what you wrote, although 280 psi seems to be a bit to close to 270 psi nominal pump pressure. this can cause a continuous flow of water through Cla Val.
Let the client make the final settings that from my experience should be in this case at least 290 psi or even 300 psi.
reviewing I found the following:As per NFPA 20 (2019) section 4.17.3 "The pressure rating of the discharge components shall be adequate for the maximum total discharge with the pump operating at shutoff and rated speed but shall not be less than the rating of the fire protection system . " therefore both components must be rated to the calculated pump shut off pressures.
That is, all components must resist or be supported at shutoff pressure.
Then in that case: Diesel 750GPM 270PSI Shutoff: 331PSI All components must be included, including the relief valve pilot at 331 PSI.
Electric 750GPM 323PSI Shutoff: 398PSI All components must go to 398 PSI including the relief valve pilot.
But I'm not sure if the electric fire pumps are too. But it makes sense, because to be able to reach 150% of the flow should revolutionize the engine and reach that flow value. What do you think about this?.
On the other hand, the pilot relief valve must be configured to the shutoff? to be able to reach 150% of the flow without leaving for the return.
good job with your research. all of this can be summarized so that both the pump and the other components must be properly selected.
PRV is your safety valve that protects your system.
Diesel 750GPM 270PSI Shutoff: 331PSI All components must be included, including the relief valve pilot at 331 PSI. - thats right, if component are rated lower than pilot must be adequate to components to protect them. Otherwise your pump is not selected properly. What we want to avoid is constant flow through PRV during normal pump operation.
Electric 750GPM 323PSI Shutoff: 398PSI All components must go to 398 PSI including the relief valve pilot. - same as above,
and answearing your question about electric fire pumps. Only electric pumps with speed controlers require pilots. The standard specifically does not permit the use of a main pressure relief valve on an electric fire pump, except where a variable speed driver is used. Variable speed drivers are required to default to constant rated speed operation. In the event the variable speed driver fails, the rated speed can result in system over-pressurization. In this case a pressure relief valve is required.
Also your designer should match the pump to the system demands, in order to avoid overpressurizing the system and then using pressure regulating devices to compensate.
Thanks Michal !!
yes you always consider closing pressure only to check if it's higher than your accessories are rated. If closing pressure is higher, then your installation is in danger and you need a pilot valve.
If you have pump with closing pressure (even nominal higher than 175 psi) at 300 psi and sprinkler heads installed with maximum allowable pressure at 175 psi then your pump must be replaced.
Always if you have sprinklers you need pilot at maksimum 175 psi.
Dear Michal Lein,
We had recently tested Fire Pumps found the issue on pump shut off pressure 250 psi which is Exceeding components rated pressure with 175 psi and diesel driven Pump and electric driven pump without variable speed control. As per NFPA 20 4.7.7, Pressure relief valve and Pressure Reducing valve not allowed in Suction and discharge to meet pressure requirements, kindly suggest a solution Please help me to get out of this issue as NFPA appreciated.
Here is the paragraph from annex of NFPA 20 that might help you.
Thanks dear kindly send me complete document NFPA 20 cant find.
I got those paragraph from NFPA 20, 2016 edition. Please see below image.
Based on this, you can used pressure reducing valve to meet the requirements of 4.7.7.
Retrieving data ...