Hopper Pressure Lower than Gun Pressure

[devinrist]

Seasons greetings to everyone!

Hi all,
I am new to this forum.

Currently I am pulling my hair out at the roots trying to solve a 'Hopper Pressure Lower than Gun Back Pressure' problem.

The system is a Metco DJ2700 using propane with Hydrogen electric start and a 9MP-DJ powder feed unit.

We had this problem before and found it to be a faulty 1 PS switch which we replaced and the problem was solved.

Now 3 months later the same error message is happening. We have checked the switch, traced the lines for leaks, checked regulators, replaced all the o-ring on gun and still the same problem.

Has anyone had the same problem and can anyone give me some advice on how to proceed from here on?

Thank you all very much!

[loriolo]

Hi Devinrist
9MP-DJ is a very complicated and crazy system, need to much maintenance and spares cost is very high, the problem you say could be problems in the Valve 9MP56379 which has 5 O'Rings the old one, and the new one has 4 O'Rings (9MP 56415), there are too many hopper O'Rings that can be damaged, to test if there is leaks, you must pressurize the system after closed inner and outer gas and powder lines, and check if the pressure gauge maintain the pressure without any change.

[ServiceTech]

Former Sulzer Metco (US) Field Service Engineer here;

First of all, contact the Field Service department and they will put you in contact with a house tech to assist you. The alarm is generated by the pressure differential switch and is caused by higher pressure down stream (gun side) than actual hopper pressure. This is a safety device to prevent gases from backing up to the hopper vessel from the gun. Until then, make sure the hopper pressure is set to at least 50 H2O or higher. You can accomplish this by entering into Hopper Pressure mode and manually inputting the pressure. The 9MP-DJ is designed to alarm with "Hopper Pressure Lower Than Gun Back Pressure" as a safe guard if the hopper pressure is set too low. Second, clean out the hopper, and run it empty, with no powder in the hopper and set to about 150 H2O. Do not light the gun!!! If the problem remains, the system is either clogged, a faulty switch pressure differential switch, faulty computer pressure relay or even a faulty EP-1. Again, best thing is to allow the Field Tech to verbally walk you through the process.

[chromalloymachi112]

Seasons greetings to everyone!

Hi all,
I am new to this forum.

Currently I am pulling my hair out at the roots trying to solve a 'Hopper Pressure Lower than Gun Back Pressure' problem.

The system is a Metco DJ2700 using propane with Hydrogen electric start and a 9MP-DJ powder feed unit.

We had this problem before and found it to be a faulty 1 PS switch which we replaced and the problem was solved.

Now 3 months later the same error message is happening. We have checked the switch, traced the lines for leaks, checked regulators, replaced all the o-ring on gun and still the same problem.

Has anyone had the same problem and can anyone give me some advice on how to proceed from here on?

Thank you all very much!

change injector shaft

[Johnny_Blaze]

Seasons greetings to everyone!

Hi all,
I am new to this forum.

Currently I am pulling my hair out at the roots trying to solve a 'Hopper Pressure Lower than Gun Back Pressure' problem.

The system is a Metco DJ2700 using propane with Hydrogen electric start and a 9MP-DJ powder feed unit.

We had this problem before and found it to be a faulty 1 PS switch which we replaced and the problem was solved.

Now 3 months later the same error message is happening. We have checked the switch, traced the lines for leaks, checked regulators, replaced all the o-ring on gun and still the same problem.

Has anyone had the same problem and can anyone give me some advice on how to proceed from here on?

Thank you all very much!

Hi chromalloymachi112,

Inspect the pinch valve for wear and tear, holes etc... change if necessary.

9MP DJ powder feeders are very reliable and not very expensive to maintain. At any point, if you have a minimum input pressure of 175PSIG and your gun pressure is higher than the hopper pressure, the first thing to check is the pinch valve, no other component sees more mechanical activity than this component, and, is the primary source for a leak...it's a small piece of surgical rubber that can wreak havoc with your powder feeder and wears out very quickly than any other component in the hopper, second, check all pneumatic connections for leaks as well...if that doesn't work and you still have erratic pressure values, the E/P valve is probably damaged...that can get expensive...but, you have to be sure that you NEVER pass a positive pressure with the coupling still attached to the feeder unit when cleaning the hopper with an air gun, always disconnect the hopper coupling from the powder unit before cleaning it with compressed air, if you don't have the intermediate filter setup on your 9MP-DJ, you will force powder into the E/P valve and damage it, which will always give you erratic pressure values and feed rate instability during operation.

Changing the powder pick-up shaft is always an option...but unless the o-rings are damaged I doubt very much that it would cause a pressure drop...pulsation in the powder flow would be a possibility, but not a pressure drop.

Regards,
J.B.

[Stephen Booth]

I have a similar problem with a 5MPE-DJ with a HH-DJ2700 running propane and oxygen gases, manual ignition

Assume we should inspect the same components:

a) O-rings, there hopper Orings that can be damaged, to test if there are leaks, you must pressurize the system after closing inner and outer gas and powder lines, and check if the pressure gauge maintains the pressure without any change.
b) all pneumatic fittings
c) Pinch valve
d) Pick up shaft and O-rings
e) Empty powder hopper and clean hopper well after disassembly to see if there is any blockages, and run the system without lighting the gun
f) check powder injector in the Gun

The powder feeder feeds normally, and accurately until its fitted to the gun, and then the powder does feed any more.