Flomatic PDP3-8 Installation Manual

Pilot Valves Installation Instructions

Model PDP ⅜”

Description:

The PDP Pressure Differential Pilot Control Valve automatically maintains a constant pressure differential between any
two pressure points in a system. It is a direct acting, spring-loaded, diaphragm type valve that operates hydraulically and
is designed to maintain a pre-set pressure differential. When used as a pilot control with a Flomatic Automatic Control
Valve, it will maintain a pressure differential sensing from across two points. See cross section drawing on back page.

Operation:

The Pressure Differential Control Valve is normally held closed by the force of the compression spring above the
diaphragm. Pressure sensing from two points, one above the diaphragm and one below the diaphragm, acts on the
diaphragm to maintain a preset pressure differential. The flow thru the valve responds to changes in differential pressure
from the two sensing points.

Installation:

Installation must be performed by qualified, licensed personnel only.

The Pressure Differential Control Valve may be installed in any position. There is one 3/8” NPT inlet port and one 3/8”
outlet port (two ports optional), for either straight or angle installation. Two ¼” NPT sensing ports, one in the spacer and
one in the cover connect to the controlling pressure. A flow arrow is marked on the body casting.

Adjustment Procedure:

The Pressure Differential Control Valve Model PDP can be adjusted to provide a pressure differential range as specified
on the data plate (5-80 PSI standard range other spring ranges are available)

Pressure adjustment is made by turning the adjustment screw (first remove plastic protective cap and loosen jam nut on
adjustment screw) to vary the spring pressure on the diaphragm. The greater the compression on the spring the greater
the pressure differential.

1. Turn the adjustment screw in (clockwise) to increase pressure differential.

2. Turn the adjustment screw out (counter-clockwise) to decrease the pressure differential. When pressure
adjustment is completed, tighten jam nut on adjustment screw and replace protective cap.

For best operation, observes the minimum flow rates given in the table are for the main valve on which the FCP is installed:

Control Valve Size 1-1/4” thru 3” 4” thru 8” 10” thru 16”

Minimum Flow GPM 15-30 50-200 300-650

Maintenance:

Annual inspection and maintenance is required of all plumbing system components. To ensure proper performance and
maximum life, the PDP must be inspected, tested and cleaned on a regular basis.

Disassembly:

To disassemble follow the sequence of the item numbers assigned to parts on the cross section drawing on the reverse
side of this sheet.

Reassembly:

Reassembly is the reverse of the disassembly. Follow this procedure:

1. Install o-ring (17) onto plug (5) and screw into body (with spring for lower spring ranges than 30 PSI). Screw the
plug in by hand. Use wrench to tighten only.

2. Install seat (4) into body (1). Use socket to tighten only.

3. Install o-ring (18) onto center groove on stem (2) and install o-ring (15) onto stem (2) in groove at the bottom of
the thread.

4. Install stem (2) into spacer (6).

5. Assemble diaphragm plate (7) onto stem (2) with the radius facing up. Install the diaphragm (14) onto the stem.

Install the second diaphragm plate (7) onto the stem (2) with the radius facing the diaphragm (14). Tighten the
hex nut (8) hand tight onto the stem (2). Using a wrench on the bottom of the stem (2) and a wrench on the hex

nut (8) tighten until snug.

6. Install o-ring (16) onto spacer (6).

7. Install spacer (6) onto body (1). Be sure to align machine screw holes with the threads in the body and position
the ¼” NPT in the spacer to its original position in order to re-attach the piping.

Danfoss Flomatic Corp, 15 Pruyn’s Island, Glens Falls, New York 12801

Phone: [phone] Fax: [phone] www.flomatic.com

Danfoss Flomatic

PDP

Rev. A

Pilot Valves Installation Instructions

Model PDP ⅜”

8. Install spring (9) with spring button (10) on top of spring.

9. Install cover (12), adjusting screw (11) with jamb nut (21) using eight machine screws (13). Be sure to align the
¼” NPT in the cover to its original position in order to re-attach the piping.

10. Install cap seal (19) onto top of cover (12) and attach metal adjustment cap (20). Using a wrench tighten the
adjusting cap until snug.

Trouble Shooting Guide

Problem: Possible Cause: Possible Solutions:

Fails to maintain a
high preset
pressure
differential.

Fails to maintain a
low preset
pressure
differential

Leakage from the
cover, adjusting
cap or vent hole

11

20

21

19

10

9

12

16

8

13

15

7

14

18

6

3

2

4

1

17

5

Information needed to order repair parts:

Pilot Model
Pilot Working Pressure

Limited One Year Warranty: Danfoss Flomatic valves are guaranteed against defects of material or workmanship

when used for the services recommended. If, in any recommended service a defect develops due to material or
workmanship, and the device is returned, freight prepaid, to Danfoss Flomatic within 12 months from date of purchase, it
will be repaired or replaced free of charge. Danfoss Flomatic’s liability shall be limited to our agreement to repair or

replacement of valve only.

No spring compression. Tighten adjusting screw to give higher pressure differential.
Damaged spring (9) Disassemble and replace spring (9).
Spring button (10) is not in place Disassemble and replace spring button (10) on top of

spring (9).
Damaged diaphragm (14) Disassemble and replace diaphragm (14).
Spring is too compressed Back off adjusting screw (11) to give a lower differential

pressure.
Mechanical seat area obstruction Disassemble and remove foreign material obstruction.
Worn disc (3) Disassemble; remove and replace stem (2).
Stem dragging on inlet nozzle Disassemble and replace diaphragm (14)
Damaged diaphragm (14) Remove cover and tighten nut (8)
Loose diaphragm nut (8) Disassemble PDP unit and replace diaphragm
Damaged diaphragm (14) Tighten cover screws (13)
Loose cover screws (13) Tighten adjusting cap (20)
Loose adjustment cap (20) Disassemble and replace spring (9).

Item # Description:

1 Body
2 Stem
3 Disc
4 Seat
5 Body Plug
6 Spacer

6.22 MAX

1.88 MAX

3.63

7 Diaphragm Plate
8 Hex Nut

9 Spring
10 Spring Button
11 Adjustment Cap
12 Cover
13 Screw
14 Diaphragm
15 O’Ring
16 O’Ring
17 O’Ring
18 O’Ring
19 Adjustment Cap Seal
20 Adjustment Cap
21 Jamb Nut

Danfoss Flomatic

1/4" NPT LOW
PRESSURE
SENSING PORT

1/4" NPT SPACER
SENSING PORT

3.13

Danfoss Flomatic Corp, 15 Pruyn’s Island, Glens Falls, New York 12801

Phone: [phone] Fax: [phone] www.flomatic.com

PDP

Rev. A