Determination of delivery pressure from pump in my Parts Washer

[supersonics29]

We want to know how can we determine the pressure of the liquid at the delivery end of the pump. We have a centrifugal pump and a 2" pipeline at the delivery end. Pump delivery performance as per catalog is 510LPM @20 mtr head to 348LPM @36mtr head.
The delivery pipe is connected to a manifold on which spray nozzles are connected around 70 Nos.
The total length of pipe from the pump outlet to the spray manifold will be approx 5 metres of which 1.5mtr is vertical & remaining horizontal.
We have mounted a pressure gauge on the line which gives a constant reading of 0.6-0.8 Kg/cm2 which is lower is lower than our expectations from a 5HP pump.
When we block the line just before the manifold, the gauge shows a reading of 3.5-4 kg/cm2.
Kindly help us determine the process of finding out the pressure in the line.
Also, If I have to select a pump that constantly delivers liquid at 3 Kg/Cm2, how do I go about the selection?

[Kelly_Bramble]

Pressure gauge at location you want to measure pressure...

[supersonics29]

Pressure gauge at location you want to measure pressure...

I already have a pressure gauge on my delivery line. This is clearly mentioned in my initial post.

[Kelly_Bramble]

I already have a pressure gauge on my delivery line. This is clearly mentioned in my initial post.

Get one you trust and believe. There are certified pressure gauges available. There is no other way to verify the exact pressure..

[Hudson]

How far does the suction side of the pump lift fluid before pressurizing it? Your pump may be expending most of its energy on the inlet side resulting in disappointing output. Is the inlet side larger in diameter? What is the pressure on the suction side?