Excess Flow Check Valve

I am a new member. My name is Amarjit Singh Kohli & I am based at New Delhi in India. I am a mechanical engineer & have my own organisation by the name " Sakha Engineers Pvt Ltd. My job function is to design LP Gas pipeline systems for supplying gas to a number of flats in a residential colony. I request the group members to help me in resolving the following issue:

1.I want to know whether one must install an Excess Flow Check Valves (EFCV) on each arm of the Cylinder Manifold of a LPG manifolded system, before the first stage pressure regulator. The LPG composition in India is about 70% butane, 25 % propane & rest other hydrocarbons & 1 kg of liquid LPG occupies a space of 0.444 m3 of vapourised LPG at NTP. The system supplies LP gas to about 150 flats.There are 52 nos LPG cylinders of 19 kg(42 lb) capacity connected to the manifold, joined together, which give a design flow rate of 0.6 kg/hr/cylinder at 5 deg c & when cylinder is 25% full. The pressure of gas in manifolds varies from 20 psig to 120 psig depending on summer or winter months. Also, when cylinders are full they can give flow rates upto 1.5 kg/hr. The max gas consumption rate ( taken as 250 gm/hr/flat) at peak load, comes to about 37.5 kg/hr (or 17 scm/hr or about 600 scf/hr). However, during lean period, say at late night the total consumption rate is no more than 7 kg/hr. The LPG consumption per day per flat is 400 gm. Only LPG vapour is drawn from cylinders & there is no possibility of any liquid LPG in the manifold system.

2. The first stage pressure regulator reduces the pressure of gas to about 10 psig after which the gas passes to the main pipeline (1" dia). There is an overpressure shut off device after the pressure regulator. Then gas passes to branch pipelines which are of smaller pipe size (3/4"). In each kitchen, the pipe size is reduced further to 1/2" & second stage pressure regulator in the kitchen reduces the pressure further to 300 millibar (0.45 psig). Before the gas metre there is an underpressure shut off device in each kitchen. The system supplies gas to about 150 flats & the furthest kitchen is situated at about 250 metres from the first stage pressure regulator. The EFCV (if recommended) is to be installed between the manifold valve and 1st stage regulator in each arm of the manifold. The distance between EFCV & PRS 1 may be 1.5 to 2 metres, whereas the distance (upstream) between EFCV & blind end of manifold is much more, say about 7 metres.

3. Due to wide fluctuations of temperature, pressure, gas withdrawal rate & gas consumption rate, the overall max gas flow rate in the manifold or the pipeline system may be 5 times than that of the minimum flow rate, in a cyclic year taking all the max limits & minimum limits accumulatively. Further, the max flow rate in the 1" pipe of 250 metre length pipeline at 15 psig is about 37 kg/hr or 17 scm/hr ie 600 scf/hr.

4 . I have two questions. One, does such a small installation require an EFCV? Second, if the answer is yes, what should be the designed flow rate at which the EFCV should close? We cannot have a different EFCV for summer & another one for winter, or different EFCV when cylinders are full & another for cylinders when they are going to be exhausted, or different EFCV at dinner time & another one at late night hours during lean period. If we instal an EFCV which is designed to stop flow at the min flow rate (during winter + lean period + when cylinders are nearly empty, then it may be close too often during summer or peak period causing frequent interruptions of gas supply. This could be dangerous because gas will bleed through the bleeder hole too frequently till equalization of pressure is achieved. If we install EFCV designed on max flow rate during summer or peak consumption period, it will never close & remain only a show piece. Having an extra valve in the highest pressure zone in manifold without serving any purpose will go against the principles of safety.

  5. The real point is:

  " IS INSTALLING AN EFCV IN CYLINDER MANIFOLD UNDER ABOVE CONDITIONS A STEP TOWARDS SAFETY OR UNSAFETY?" [Non-text portions of this message have been removed] Received on Wed May 24 02:45:00 2006