Dry Systems Flashcards
prevent freezing
listed heat tracing
Insulate the piping
Air pressure alarm(supervisory)
optional
sends a signal to the alarm panel if the pressure in the system is to high or to low
differential dry pipe ratio
5:1 ratio
16psi air required -> 80 psi water
air seat 5x surface area of the water seat
Piston lever latch dry valve
the plunger or piston is activated to release the latch and the clapper when the built-in differential mechanism and/or external device sense a drop in system air pressure
Not very common anymore. Unrealiable.
Quick opening device
Accelerators
- differential DPV, the air or nitrogen under pressure passes through the accelerator and into the intermediate chamber of the dry pipe valve forcing the clapper to open faster.
- Piston latch lever DPV, the accelerator expels the air from the actuator achieving quicker operation.
It is imperative that the quick opening device be installed as close to the dry valve as possible.
Quick opening device
Exhauster
Not installed anymore
Exhausters are located at the end of the cross main. Commonly a 2” hole to remove faster so that the valve can trip faster.
air pressure
20 psi > calculated trip pressure
minimum 1/2” piping
Air maintenance device(listed) to control pressure if required.
compressor
cut in
cut out
cut-in 5psi below the system pressure
cut-out recommended system pressure or 20 psi above trip
air supply
replenish normal system pressure within 30 minutes
for systems protecting areas below 5 degree F(-15 degrees C) it shall be within 60 minutes.
Dry valve out of a service
call monitoring company and fire department
close supply valve
close alarm line valve and alarm test valve
close air inlet
open drain
dry valve into service
- close alarm line, close alarm test line - ensure lines are drained
- ensure system is drained
- may need to open cover to unlatch clapper, ensure condition of clapper is good
- reset clapper
- prime clapper if required
- open air valve and fill system with air, watch the air gauge.
- once full of air; close drain valve and then reopen slightly
- open main control valve slowly, as water starts to flow close the drain valve slowly
- allow system to fill to city pressure - ensure the system pressure does not rise, if so, the clapper is not set
- once system pressure is at the required pressure open the alarm line
sprinklers in a dry system
upright
listed dry sprinklers
listed residential
pendent if within a heated area and on return bends
sidewalls arranged so the water is not trapped
with copper or cpvc(non-corrosive) piping
pendants and sidewalls are allowed when not on return bends, but still only in heated spaces
flow test
not more than 60 seconds
15 seconds for dwelling units
the test begins when the test connection valve is fully opened on a system at normal working air pressure
approved calculation program - times can be calculated, as per NFPA.
max system area limitations
dry systems <= 500 gal
shall not require a quick opening device
shall not be required to meet any specific water delivery requirements.
dry systems <= 750 gal
if installed with a QOD: shall not be required to meet any specific water delivery requirements
if not installed with a QOD: shall meet specific water delivery requirements.
Drainage
non-refrigerated
branch lines 1/2” per 10’
mains 1/4” per 10’
refrigerated
branch + main 1/2” per 10’
auxiliary drains
<5 gal trapped = 1/2” valve-nip/plug
If refrigerated space must be 1”
> = 5 gals use drum drip configuration
tie in drains 1” pitched at 1/2” per 10’ for multiple trapped branch lines
nitrogen
stored pressure - tanks prefilled with nitrogen
nitrogen generator - generated on-site as required(removes o2 from the air)
requires: pressure regulator, an air maintenance device specifically listed for such a device
refrigerated space
below or at 32 degree f (0 degrees C)
Air dryers
prevent the formation of ice blocks by lowering the moisture in the air supply
4-stage air desiccant air-drying system (most reliable)
eliminate condensation which leads to ice blocks
dry pipe or preaction system is required when temperatures are below…
40 degrees F
4 degree C
Tests
quarterly tests:
test low air, priming level, accelerator/QOD
semi annual:
test electrical alarms, and tampers
annual
pressure drop test
trip test - make sure valve will trip
3 year test: full trip - flow out of inspectors test
