I am new to this forum. I am a Process Systems Engineer with about 2 years of experience. I am working on system design for a crude oil pumping application. My question is:

This system has 4 X 33% high capacity-high head centrifugal pumps. Each pump has a dedicated discharge flow control valve and also a dedicated controlled minimum recirculation line. The pumps have 50% minimum continuous flow requirements. I am having difficulty in designing the system without actually knowing how the pumps are going to be operated right from start to completion. What will be the sequence of events (closing & opening of valves, switching on/off of pump motor, etc) from start-up to normal operating and from normal operating to shut-off? Under what conditions, the recirculation line and the main line (combined from all pump discharge lines) will be active and inactive?

Please share your experience on multiple parallel operating pumps.

Dear my friendYou want to ask about the recirculation line of pump system, don't you?From my point of view, there are 3 main types of recirculation line to maintain minimum flow:- Use control valve

- Use ARV (automatic recirculation valve)

- Use RO

Using Control valve and Restriction Orifice, I think that it is quite clear.For ARV case: The function of ARV is illustrated in this diagram below.

For operation of the ARV, there are 3 cases this valve.You can see the file below to get more clear information about this cases.

I'm not sure that you get all informations which you are not clear about your problem.But if you have any trouble, please reply or send email to me. We will continue discuss about this problem.

Let's share, to be shared.

Good luck.Best regards.LuuQuocDaiEmail: luuquocdai@gmail.comTel: 0084988521012Thank you for your reply.

This is a case where control valve is used in recirculation line. Can you please explain how the plant operator will start these pumps, bring the system to normal operation and finally switch-off when pumping is complete? It has three pumps operating in parallel and the system is for intermittent use only. (once in 7 days)

I have never worked in a plant and don't know how pumps are started/stopped.Dear my friend.You want to ask how to start up pump in your system, don't you?I am not clear about your system, then I don't know how to explain to you.In general, we always make and follow a procedure for start up and shut off a pump system or a plant.For example:

With centrifugal pump, we have many main steps as follows(1) Check items in generala) Earth connectionb)Coupling connectionc) Coupling coverd) Foundation bolte) Pressure gaugef) Lubrication oilg) Housekeeping around....(2)Start up pump(a)Make sure the discharge valve is closed.(b)Open the vent valve if necessary, and make sure that the pump isAfter that, please Fill with liquid.Open the cooling water valves and make sure that the proper amount of water is flowing. Open the flushing oil valves.(d)Turn the rotor by hand to make sure of smooth rotation.(e)Fully open the suction valve.(f)Start the motor & check leakage from seals or packing.(g)After confirming gradual increase of discharge pressure, open the discharge valve slowly and completely.(h)If leakage is found, stop the pump and repair.

Another way, there are some items which you have to check during pump is running

(a)Bearing temperature(b)Lubricating oil level in the reservoir (or tank) and the amount of grease in the grease cup.Flow of cooling water(d)Suction and discharge pressure.(e)Noise and vibration.(f)Leakage from seals or other connections.If abnormal conditions are observed, stop the pump by switching over to the spare under the supervisors instructions.

Shut off procedure:(1)Close the discharge valve.(2)Stop the motor.(3)Stop the cooling water and the flushing oil.(4)Drain out the pump as required.

For other types of pump(displacement type or others), the procedure is quite similar, but there are some point you have to pay attention for this type.I hope that everything's which I said is clear enough for you.If you have any question, please post reply or send email to me. We will continue discussing about it.

P/S: This procedure is checked by a Commissioning Supervisor in our company.I think that it was quite perfect.

In minimum flow control through pump using Control valve ,i have seen many variations of control loop configurations . In some FE/FT is located upstream of recirculation tapping in some it is downstream of recirculation tapping, can u please advantages disadvantages in this two.Dear my friendCan you explain more clear about your question?Actually, I don't understand what do you want to ask?You mean that we can put FT/FE in the upstream and the downstream of recirculation tapping, don't you?My problem which I said is illustrated in the picture belows.

FT/FE in the sketch shown is in the downstream of recirculation tapping.& upstream If it in just immediate of pump discharge before Tee joint for recirculation pipe.please tell how the control loop will be formed in these two cases.Gold : I think as per all cases i have seen, FE/FT should be considered upstream of recirculation tapping,because FALL on the same FE/FT activated an interlock shutting down the pump and if FE/FT being considered downstream of tapping ,the flowrate may pass through min flow FV has not been accounted.

How do we decide whether to use dedicated or a combined min. recirculation lines for multiple pumps operating in parallel.

Example : If there 4 X 33% pumps, should we have 4 min recirculation lines branching off from each pump's discharge or a single line branching from the combined line after adding all the pump discharge?Dear my friendsAbout your questions, I have to remind you that, the function of minimum flow is protect pump.With this function, you have to minimum flow for all pumps in 3 pumps system.After that, all minimum flows will combine and return to suction equipment.Normally, with 3 pumps system, 1 pump is in stand by state.Just my opinion. If you find any mistakes in my sentences which I posted, please let's me know.Thanks in advance.