High pressure at the pump for a chilled water system

Hi,
We have a chilled water system. Primary pump loop and secondary pump loop. There are three secondary loop pumps "pumps are supplying the buildings". They the pressure gauge at every pump is reading 100 psi at their suction and 48 psi at their discharge. We do not have high pressure head and according to our calculations it should be around 50psi. The primary pumps have a pressure of 45 psi at each pump "there are three pumps". My question is: why the pressure before the secondary pumps is high? Does this mean that the secondary pumps selection is wrong? could it be that the secondary pumps gallon per minute is smaller than what is running through them?
Please help

Thank you

Mack

is rotation correct on the pumps, are the pumps fitted the correct way-ie arrow to display direction of flow?

Yes, The rotation is good

with your 3 pumps off does the pressure equalize,how is it when u start each pump up 1 by 1

It baffles me for real, I can not think of an answer. Why the pressure before a pump would be higher? I'm thinking maybe there is too much water being pushed to the suction and the pump is not designed to handle and supply all this water and this creates higher pressure at its suction. But again maybe there is more to it

I do not dare to stop any pump. The hotel manager brought me in to take a look and he does not want me to trouble the system. but, what are you thinking of by stopping the system

To overcome system loses and pressure drop across heat exchangers

Remember, this is the secondary loop. So most likely if I stop those three secondary pumps the pressure will equalize and we still have the primary pumps working

Pressure drop across the heat exchanger is not at play here. What is at play is the primary pump loop and the GPM going through the secondary pump loop, I would think

Any thoughts! To recap, The primary pumps "three of them" are 45psi at their suction and 48 at their discharge. These are the pumps for the chiller loop. The secondary pumps supplying the buildings are reading 100 psi for the suction and 48psi for the discharge, why the suction is that high?

The reading of 100psi must be wrong unless the secondary pumps are piped up the wrong way around.]

If your primary loop is at 48psi and there is nothing in the loop to generate another 52psi then 100psi is false.

Remove one of the 100psi gauges and check it with one of the 48psi gauges.

Confirm that the pumps are correctly installed.

Question is where are the measurements taken from, what is the method of measurement and what is between the two readings of the secondary pump. There could be a blocked strainer between the suction and discharge of the pump. If it is measured with an electronic transducer the signals could be mixed up. The primary system should always have a greater pressure than the secondary from experience about 10% - 20%.

I also agree with you Tesla , check the reliability of pressure gauges or another equipment you are using for measuring pressure values.Are the pipelines valves in desired position ? Is the pressure gauge installed before and after the valves on Suction and Discharge line. How much amperes pump are taking and the motor is of how many HP ?

So let me ask something, if the secondary pumps have been wrongly selected and they are below GPM "Gallon per minute" capacity, and if the primary pumps are selected right, wouldn't this mean that a large amount of water are being sent to the secondary pumps but because the pumps are small they can not handle that much water and this is why the suction pressure is a lot higher than the discharge pressure?
I checked all the pressure gauges and switched them and the readings stand. The pumps are installed right.

Where is the expansion tank teed in?

How close are the tees for off the primary S-S-S-S and R-R-R-R or is it teed S-R-S-R

Regardless of what the primary pressure is the secondary pressure must be greater, read up on pump laws.

So many questions here and I have another one. What type of system is it? Decouple pipe, injector, or bypass? If it were possible for a simple line diagram of the system it would be very helpful.

A drawing would be nice.
Could it be that your gauges have some tails penetrating into the pipe work, on the suction side facing the flow so measuring velocity pressure plus static pressure. On the discharge the pipe is with the flow, causing a vacuum on the pipe, static less the vacuum.

Gentlemen,
The installation at this project is unique, when I say unique I mean I never saw such an installation. The return is going to three primary pumps. The three pumps are connected to one large pipe. This pipe is splitting to supply the first chiller and then splitting to the next chiller and then to the last chiller. The pipes out from each chiller are connected to one pipe which is going to the secondary pumps loop. The pipe is split into three branches each is going to a separate pump. No by-pass, no pressurization tank. The expansion tank is installed close to the primary pumps.

Can you post a few pictures or a diagram .It would make things a lot easier.
Cheers
Stu

are all 3 secondary pumps pulling the same running amps?

i was hoping you would let us know where the exp tank is, suction or discharge of the primary pumps. It is quite important to see each component as it relates to all others, with rough dimensions. I have some ideas but they won't mean much without that info.

Picture please, is worth 1000 words