【 Weak current College 】 fire protection water supply problems of pressure and pressure relief

Introduction: overpressure in the fire protection water supply objective existence, to the detriment of fire water system. Analysis of the causes of caused overpressure, and taking measures against overpressure, and on the application of specific relief.
Keywords: pressure relief valves-pressure relief vent flow

1 causes of fire water system overpressure
The tall buildings design fire protection standard (GB50045-95) section 7.5.6 stipulates: "the high-rise building water systems should take measures to prevent overpressure." This is my first time pressure and prevent overpressure measures included in the specification section. Fire water system overpressure is the system pressure exceeding the working pressure limits, creating pipelines, fittings, accessories, materials and equipment damage, affect the normal operation of fire water system. Overpressure in the fire protection water supply objective existence, needs attention, and to take countermeasures.
Fire water system overpressure were in the following circumstances:
(1) according to the selected design flow, and fire pumps pump flow ~ lift curve less steep, when the fire pump in the small flow operation overpressure occurs. Small flow operation means the fire early and fire pump post. At this point, fire-fighting facilities yield smaller, fire hydrant's water gun for 1 ~ 2, sprinkler system nozzle for 1 ~ 3.
(2) the fire pump water directly from the water supply network, pump lift by minimum water pressure water supply network. Water pump run time such as when the maximum water supply network pressure, while the lowest water supply network pressure and maximum pressure difference is large, there is excess pressure.
(3) fire-fighting water supply pipe network according to the lowest position of indoor hydrant hydrostatic pressure 0.80MPa for vertical division, the network has not taken a perfect vacuum, when the fire pump is started, the network will be due to the lower portion of the fire hydrants in dynamic pressure value is greater than the static pressure value and bursting.
(4) the fire pump due to failure or power outage and suddenly stopped caused overpressure hammer.
(5) fire water valve vertical partitions use feedwater manner, when the section valve is closed due to a fault, or bypass pipe on valve control, will cause the next area of overpressure water distribution system.
(6) the fire water use feedwater pump pump counterpart, that is, the next area of pump outlet and the District of pump suction pipe direct connection, when the check valve does not close, the following areas of the pump will vary depending on the hydrostatic pressure is greater than the working pressure and pressure.
(7) voltage pump low bit is set, its suction pipe to quotations from high water tank, when the hydrostatic pressure is greater than the working pressure is bursting.
(8) fire-fighting water supply vertical division of the district and the area of common pump adapter, when you check valve to prevent the string compression does not close, the following would occur and overpressure.
(9) set or range, is equipped with voltage pump or air pressure tank temporary high pressure water supply system, due to the long pipe head loss value is large, fire-fighting water supply voltage value on fire hydrant, fire-fighting facilities cause pressure.
(10) the fire truck vehicle fire pump series running water supply to the pump adapter caused overpressure indoor fire water network.
(11) the actual lift fire pumps and a sample of the product, and the deviation of the larger, caused overpressure.
(12) water distribution valve set incorrectly or do not set the exhaust valve, the gas pipeline network memory has the role of the external force is in the compresses State caused overpressure.

2 the measures against overpressure
12 overpressures, and water pump related accounts 8. At present domestic measures taken against overpressure, as follows:
2.1 take technical measures to prevent overpressure generation
(1) selection flow ~ lift curve gentle water pump, one worthy of recommendation is: building fire special pump (formerly tangent pump), flow ~ lift curve special flat, assumes constant state.
(2) use multiple pumps, small when you run a small pump flow or single pump operation, high flow, big pump operation or more pumps in parallel operation.
(3) the fire water pipe vertical partitions, not complying with the minimum position 0.80MPa indoor hydrant hydrostatic pressure, due to partition space; or press 0.80MPa value vertical partitions, but to take the appropriate measures of effective decompression.
(4) adopt constant pressure variable flow pump supply frequency adjusting speed, so that the water pump water pressure variation in flow remains constant.
(5) the fire pump water directly from the water distribution network, to the maximum of water supply network pressure on the pump's work check to prevent overpressure.
(6) the adoption of the water way pressure reducing valves partition, when there may be pressure valve failure or bypass pipe valve control and overpressure, no by-pass pipe, pressure relief valve-set.
(7) pumps the water-supply mode counterpart pumping water distribution system, or top and bottom area common pump adapter when using high-quality water tight performance good check valve.
(8) voltage pump low bit is set, the suction pipe from the fire pool attracts can prevent overpressure.
(9) the pump outlet check valve set speed traps and other devices, you can effectively prevent the hammer.
2.2 throughout the fire water supply system of carrying capacity
So in normal circumstances occur, the ability to increase pressure on the allow working pressure range.
2.3 take appropriate relief and regulated facilities to overpressure values does not cause damage
Pressure relief and voltage facilities have reflux pipe, safety valve, pressure relief valves, steady voltage valve, pressure tank, etc. Under revision by the sprinkler system design specifications "in the relevant provisions of the settings for the drain valve.
Proven pressure relief valves responsive, accurate, reliable, and can effectively prevent overpressure. Pressure relief valves in the application, you should be aware of the following two questions:
2.3.1 setting location
The fire pump pressure relief valves set in, or in a outlet check valve (along the fluent direction) or check valve, or before or afterCan effectively prevent (1), (2), (6) for reasons caused by the overpressure. But hammer or network memory gas resulting from the pressure relief valve when located to effective prevention. Therefore, the best location for relief should be in the pump outlet check valve.
2.3.2 drain valve caliber
Drain valve diameter directly influence water pump operation point and its actual head and flow.
Figure 1 H ~ Q for water pump flow ~ lift curve, RAB is AB pipe resistance curves, point b, the pressure set point into Q ' discharge. Starting from Q ' for the BC segment of resistance curve RBC, RBC RAB and tandem synthesis resistance curve R, R, and h-Q a curve point M to pump operating point.

Figure 1 (on)
We know from Figure 1, the greater the pressure relief valves-Q value increases, the more RBC's location, on the right side of the series R curve position after the more low, where M is the lower. Therefore, pressure relief valves of diameter directly determine pump operating point, directly determine pump head and flow, in general the diameter and pressure pump outlet pipe of the same size or smaller. Because R curve above RAB RAB and RBC, is the series combination curve, so there is no need to worry about M operating point is lower than the pump pressure relief valves-free original operating point.