pressurized tank / safety shower 2

[wittyish]

Greetings,

I'm looking for feedback on method.

We have a 400 gallon tank (160psi mwp)and a safety shower with a required pressure of 30 psi. There is 5 psi of pressure loss between the tank and shower. We use 2 air cylinders (80 ft^2 @ 2200 psi) to a regulator set at 35 psi to pressurize the tank and supply the shower for 15 minutes @ 25 GPM. (I am having a hard time finding the equations, but test data confirms)

Now if the new pressure loss is 40 psi; is it as simple as doubling the air cylinders to 4 x 80ft^2 @ 2200 psi and setting the regulator at 70 psi?

Best Regards,

 

[TD2K]

The 40 psi is the new pressure drop between the tank and the shower? Your approach is correct. Is the shower able to handle the 70 psig pressure it will see under no flow conditions?

Also, if this tank also supplies the first shower with the 5 psi line loss, it's going to use more water when it is used because it will now see a higher inlet pressure because the tank is maintained at 70 psig, a quick check suggests the first shower would flow about 35 gpm.

Check also the regulators you want to use, droop might be a factor that you have to adjust for.

 

[wittyish]

Yes, the new pressure drop is 40 psi b/t the tank and shower. The shower can handle 70 psi no flow. How did you figure the new flow to be 35 gpm @ the 1st shower?

Thanks,

 

[TD2K]

For something like this, I just do a trial and error. Guess a new flow, figure out the hydraulics and then see how it compares to my new basis. In this case, 70 psig in the tank.

The first shower flows 25 gpm when supplied with 30 psig water. For most devices in liquid service, flow is proportional to the square of the pressure drop. Double the flow, you need 4x the pressure drop.

You had 35 psig in the tank with 5 psi line losses giving 30 psig at the shower head before you added the second shower with the longer line and had to increase the tank pressure to 70 psig.

Let's assume the new flow to the first shower is 35 gpm flow, that's 40% more flow which in turn requires 1.96 (call it twice) of the pressure drop or 60 psig at the shower. You also have twice the line losses to flow that extra water or 10 psi. Total is 70 psig. If this value is higher or lower than what you will hold the tank at, you adjust the flow and work through the hydraulics again. You could also set an equation and solve for the flow explicitly.

 

[chicopee]

First, I would like to know what is the max. allowable pressure of the 400 gallon tank to which you are going to pressurize?

 

[MJCronin]

witty....

Have you considered purchasing a pre-designed, certified "tank shower" ?

http://www.hughes-north-america.com/tank-showers.html

Several vendors offer these units that will supply the propper volume and temperature of water necessary...