Restriction Orifice

Instead of a fixed orifice, you might also consider a needle or expansion valve, which can be adjusted for various conditions.

Some pump manufacturers may have already designed a suitable "Q-max" orifice in advance, and furnish it as part of the total pump package. (I have worked with refrigerant pumps where this approach was taken.)

If you present this same question to some pump suppliers, they will quite likely be able to advise you. (If you give them full datails of your piping.)

There are variable orifices. They are called "valves".

You can add more bend to come around 290MLC. calculate the extra bends and length and reroute your piping.

GA

With a VFD he can keep the same pump (no impeller reduction...) and tune the speed (rpm) to achieve the same flow at the back pressure available.

I see no actual calcs yet. Try this site...very good.

www.pipeflowcalculations.com

If the excess of pressure at the end is a temporary condition, I would suggest to use a valve (it is known as "throttle adjusting") .

If this condition remains above certain amount of or all the time, the use of a VFD is advisable technically and economically.

Also change the motor for one of a lower speed (check thoroughly!) could do.

To evaluate economically, check: estimated running time, VFD cost, valve cost, new slower motor cost, electrical savings for each case (I would say you could save around 50% with the VFD or new motor), , and make your maths to find the more convenient solution.

Dear santoshp9, are you listening the advices of learned members, please respond.

If you are yet to lay 80 NB pipe, so far only thinking and calculating then I have one more advise to offer. Change your plan for 50 NB pipe and fittings. You will get double benefit, higher resistance with much lower cost.

Dear sir,

If I go for 50 NB pipe the velocity through it will be around 4.5m/s.There is chances of errosion of pipe.Recommended velocity for 50NB pipe is not more than 1.5m/s as per design criteria.

You have got many practical solution to your problem. Now comes the next step to choose most appropriate solution which can give you intial as well as running economics suitable to the system. VFD is costly afair but if your requirement needs frequent changes in flow and head then go for VFD. Changing motor RPM seems most suitable solution as well as you can try using smaller impeller but lower RPM machine's wear and tears are less and pump runs more stable.

No, your calculation seems to be wrong. For 50 NB pipe the velocity through it will be around 2.5 m/s for your required flow rate of 20 m3/hr. Piping velocity of 2-3 m/s is OK for your application.

I agree with this. Keep the velocity less than 1.5 m/s. Higher velocity brings in other factors which need be considered (such as water hammer - although at NB50/80 you're pretty safe). From my experience, keep the velocity less than 1.5 m/s (and it solves many issues).

Cheers

Anthony

I'm not sure what type of pump you have purchased, but if it is a centrifugal pump you can have the pump supplier "trim" the pump impeller in order to get to the design duty point. This would be the cheapest alternative for you. Otherwise if you can swallow the outrageous cost go for a different motor size or VSD.Remember, most pump distributors will charge you a "Restocking" fee for returning any pump or motor.....basically it's highway robbery IMO by the bastards and just pads their profit margin (sounds like a bank and their service charges, eh????)

According to pump laws for same speed flow is proportional to the diameter and head is proportional to square of diameter. Trimming the impeller without examining the characteristics of the pump will bring down the flow although the head will be achieved.