Pump or valve first?

Hi there, not sure if there is a correct order to this. I am writing a function that will turn on a pump and open a solenoid. should I open the solenoid first then turn on the pump or vice versa? Or turn them on at the exact same time?

Just curious, not sure if there is a right answer or not.

In most cases it probably doesn't make any difference, but I'm sure there are a few cases where it does. And among those cases I expect there are some where the pump should be on before the valve opens and some where the valve should be first.

It depends on the type of pump starting a PDP type before opening the valve or closing the valve before stopping the pump may damage it. in general, you open the valve, then start the pump, stop the pump and close the valve in that order to prevent over pressurising any equipment in the line like a plated heat exchanger etc. But again it depends on a lot of factors.

My opinion

I always open the solenoid first to ensure that you don't dry run or dead head a pump.

Lots of factors to consider....


1. Positive Displacement Pumps : Any type of pump that has a "moving cavity", eg Gear-Pumps, Peristaltic Pumps, Worm Pumps, etc. falls into the PDP family.

Since fluids are generally in-compressible, something will break, rupture, or spring a leak.

You MUST prove both the feed route open and the delivery route open before starting : don't do them both at the same time.

Having said that, nearly all PDP installations I have seen have a relief valve from delivery back to the suction line. I personally would not use "solenoid valves" without feedbacks on PDP installations.



2. Centrifugal Pumps : The most common practice is to open valves, then start pumps. However there are times when you must prevent back-flow, so starting the pump first is in order, then opening the valve(s).

It is preferable NOT to keep valves shut on the suction side of a CF pump. You will generate negative pressure, and I have seen many times that the valve will then not open.

You most certainly can run a CF pump into a "dead end" without damage

Is the valve before or after the pump?

One thing to consider if it is after is to shut the pump off so it stops producing significant pressure before closing the valve otherwise there may be a considerable pressure surge.

If it is before the pump then it may be best to keep open until the pump stops significantly pulling, or it could cause a suction/negative pressure before the pump.

As for turning ON it would depend on the pump and plumbing setup and characteristics. Daba's advice covers that well.

A couple of additions:

Many centrifugal pumps can be dead-headed, but for most of the time must be kept short to avoid overheating and physical damage to the pump.

Ifyou want to prevent backflow from the system through the pump I'd suggest using a check valve. That will allow you to open the discharge isolation valve before starting the pump.

I would only use a valve on the pump suction for isolation during maintenance. During normal circumstances it should be open. Starting a pump with a closed suction valve is a good way to induce cavitation and early pump failure.

Wow! I'm impressed.

Those were some really good and informative answers from you guys.

If there is a high pressure differential across the pump outlet valve AND the pump is centrifugal, you may want to start and bring the pump speed up until the differential pressure is low prior to opening the valve.

Bit_Bucket_07 said:

Wow! I'm impressed.

Those were some really good and informative answers from you guys.

Click to expand...

It's called: "Been There, Done That"

Tom Jenkins said:

A couple of additions:

Many centrifugal pumps can be dead-headed, but for most of the time must be kept short to avoid overheating and physical damage to the pump. (1)

Ifyou want to prevent backflow from the system through the pump I'd suggest using a check valve. That will allow you to open the discharge isolation valve before starting the pump. (2)

I would only use a valve on the pump suction for isolation during maintenance. During normal circumstances it should be open. Starting a pump with a closed suction valve is a good way to induce cavitation and early pump failure. (3)

Click to expand...

(1) I once worked on a High Temperature Hot Water (HTHW) system that ran 24/7. 3 out of 4 pumps recirculated the water, and 2 out of 3 just kept the system pressurised to 3 bar +. The water was heated to about 130 deg.C, so the pressure had to be maintained. The only time there was any flow through the pressurisation pumps was when HTHW was drawn from the recirculating main.

(2) Check-valves, or non-return valves, are generally frowned upon in process industries. They are sometimes difficult to CIP (Clean In Place), leading to longer cycle times, and introduce a flow restriction which has to be accounted for by increasing the size of pumps.

(3) Pumps are very often used for multiple source vessels, a CIP set for example, will have (at the very least) a Pre-Rinse Tank, a Detergent Tank, a neutralising Acid Tank, and a Final Rinse Tank. Valving is then used to deliver to one pump.

Many pumps don't like to be run "dry", so opening the route and waiting to detect flow ensures the pump is flooded before starting it. CIP "Scavenge" pumps, on the other hand, which are used for keeping the vessel you are cleaning as empty as possible, are therefore designed to run with minimum "flooding" of the pump cavity.


Summarising - You must always check with the pump manufacturers, let them know and understand your applications. If you just go ahead and use a pump without verification from them, any warranties will almost certainly be null and void.

Your plant layout and geometry will also have an impact on your choice of pump for any given application.

To prevent cavitation, which destroys pumps in remarkably short times, you have to maintain a "Net Positive Suction Head" (NPSH) on the pump inlet.


This article explains NPSH very well.

If vacuum pump. Start pump first to establish vacuum (and to keep from sucking oil out of pump) then open valve..

NetNathan said:

If vacuum pump. Start pump first to establish vacuum (and to keep from sucking oil out of pump) then open valve..

Click to expand...

That assertion is too simplified.

If you were using double-seat mixproof valves (in a valve block, for example), you would necessarily connect the bottom port to the suction of the pump, otherwise the suction would open a top port.

But the suction generated could "lock" that bottom port such that it would be impossible to open it.


EDIT: I have also witnessed butterfly and ball valves become locked due to pressure differences either side of the valve.


It's a question of "horses for courses", you do whatever you have to do, taking into account plant design, geometry, and the parts used.

One size does not fit all eventualities, and sometimes compromises have to be made ....

daba said:

That assertion is too simplified.

If you were using double-seat mixproof valves (in a valve block, for example), you would necessarily connect the bottom port to the suction of the pump, otherwise the suction would open a top port.

But the suction generated could "lock" that bottom port such that it would be impossible to open it.


EDIT: I have also witnessed butterfly and ball valves become locked due to pressure differences either side of the valve.


It's a question of "horses for courses", you do whatever you have to do, taking into account plant design, geometry, and the parts used.

One size does not fit all eventualities, and sometimes compromises have to be made ....

Click to expand...

Been using vacuum rated butterfly valves, ball valves and solenoid valves for decades.
If they are rated properly, and installed correctly, they will open and close under vacuum (it is only 14.7 psi differential).
Most of the time, you do not want to expose the vacuum line above the valve to air, contaminating the line and causing an unwanted rise in pressure also, or pump oil sucked into the line.